Technology could develop, arguably would automatically, if aquatic creatures reached a certain brain size.
The first major impediment to the formation of technology underwater is the lack of oxygen. Water in general is not an efficient solvent of oxygen for example, a human would need gills several times their body area IIRC something over 15 square meters in order to exact enough oxygen from even well oxygenated water. There are plastics that form osmotic membranes in water that selectively pass gasses but not water. Ordinary polystyrene will do this. But you need such a large surface area that nobody had been able to make a practical breather.
There is also the problem that oxygen content varies significantly with depth and vertical and lateral currents. Sometimes, fish hit a dead zone and simply suffocate before they can swim out.
That's the biggest brains in the sea belong to aquatic air breathing mammals. Gils just won't cut it. The biggest non-mammal brains belong to octopi who "breathe" by inhaling a lot of water, compressing it then jetting it out again. Even so, they are limited to brains much smaller than mammals.
Postulating alternative chemistries really doesn't help because such chemistries won't have the energy flow of an oxygen based one and therefore couldn't support large, energy intensive brains. An ecology based on sulfur compounds, like those in "black smoker vents" won't likely support large brains.
Better to postulate an alternate neurology which use a different and lower energy mechanism than electrically charged membranes. Can't think of plausible one off the top of my head.
So, you're probably looking at something that is air breathing or as some other means of obtaining excess oxygen e.g. has symbiotic plants that generate or cache oxygen for it in a form like hemoglobin. Air breathing doesn't require land. Many surface dwelling fish have a primitive air breathing system from absorbing oxygen from swallowed air. Lung fish breath through their gas bladders which are attaches to their digestive track. Something similar could evolve eventually to air breathing "fish" with no land ancestry.
The other problem is the vast majority of the ocean floor is a desert. Once you get down passed 60-70 meters, there is no light for photosynthesis and away from the continents, there isn't a lot of minerals, like iron, floating around. The seas both in terms of area and volume, are relatively dead.
So, the planet would need broad, shallow (<100 meters or so) oceans like those which dominated earth in the permian.
Hands or manipulators are not much of problem. If you look at fish, octopi, anemone and other organisms that live in and on coral reefs in shallow water, it's clear that streamlining isn't much of selection pressure. Speed is important in the open but in more confined spaces, the ability to maneuver precisely, anchor and push-off seems more important. Octopi, for example, have manipulators on par with human hands.
Besides there are options to hands. You could have a hive species that uses swarm tactics, like bees, ants etc do, using the coordination motion of dozens of individuals to provide all the control vectors. Swarm robots are all the rage now because it's a lot easier to control and object with a lot of small controlled shoved that trying to control it with large vectors arising from a single point, e.g. a human shoulder joint giving rise to all the vectors of the arm and fingers.
So, once you have big brains and manipulators what could you make?
Aquatic species primary senses would likely be those that work best underwater, sonar, electrical fields, combined smell/taste, ambient vibration detection etc. Visible light vision would be a secondary sense. The underwater senses would likely give a sentient species something close to x-ray vision. Dolphins and whales appear able to scan the insides of living animals with their sonar. Likewise they can detect buried objects. Electrical field detection likewise gives the ability to detect living organisms and some structures in sand and coral. Smell and taste sensors wouldn't be limited to the mouth or nose but could be spread out all over the body or concentrated in manipulators.
In short an aquatic species could extract a lot more detail about objects in their environment, especially the chemical, electrical and internal structure, than air/land based could.
So, they could examine their environment and manipulate, the question is why bother? As much as we like to flatter ourselves, intelligence isn't always an automatic game winner, especially when it comes from such high metabolic overheard. It requires a payoff. For humans, it was cooperative hunting/scavenging for meats and fats, combined with stone tools to cut up tissues and bones that our muscles, jaws and teeth could not. Lastly, fire let us digest a wider range of nutrients without any metabolic or structural specialization similar to that found e.g. in vultures.
It really looks like the primary driver of large brains is not technology, but social coordination. Large brains let animals work in larger and more effective teams. E.g. wolves, meerkats, dolphins etc all have large brains compared equivalent more solitary species but they don't use technology as we think of it. (Dolphins seem to use their large brains to plan and carry out gruesome coordinated military campaigns against other dolphins, largely for kidnapping females. Most dolphins are killed by other dolphins instead of predators. Those scars are from bar fights. "Flipper" they ain't.)
In the same way, large brains might get started in an aquatic environment because of a need for coordination. That could be some form of hunting but it could also be obtaining oxygen or creating reefs for symbiotic food species and defense.
Imagine a bunch of air breathing octopi, whose primary primitive technology was building coral reef structures to provide air, food and shelter. From there, they could figure out how to make cutting weapons from coral.
Tools underwater would be much different than we think of them. For example, swinging a lever like an hammer or axe, is not efficient under water because water resistance robs all the energy. Plus, rapid high energy motions stir up silt and generate vibrations that telegraph one's position.
Instead, grinding, raking and drilling would be the orders of the day. Repetitive motions over short ranges would work better than rapidly moving levers. Water jets, with or without injected abrasives, could take the place of knives and saws.
Various forms of bicarbonate and biosilicate would likely take the place of stones. Likely, a form of coral topiary would be an early technology on par with making mud bricks was for humans.
Rocks, especially specific types like flint, might be hard to find because in the sea, everything gets covered with silt and biomatter. On land, plants needs a certain minimal amount of soil and won't grow on bare rock save in very humid conditions. In the ocean, however, plants, fungi and sessile animals simply use hard objects as anchor points. On land, a pile of flint will have not plants it and will be easy to spot. In the sea, it will be covered up with something. Nothing will just laying around.
On the other hand, as noted above, sentient sea life can probably probe through materials so perhaps it wouldn't be that much of problem.
It's important to remember that you don't need as strong of materials to build underwater as on land. Building on land requires materials with great compressive strength because air is compressible and provides little buoyancy. Air provides no structural support at all. All the strength comes from the materials. (Foams with trapped air are an exception but they are weak because they compress.) On land, to lift something you have to put a lot of compression resistant mass under it e.g. stone, steel etc. Under the water, you attach a balloon to it and lift it up. If you want something to resist compression, you make a sealed cell of a high tension material and then let the incompressibility of water carry the load.
The structures of an underwater civilization would likely be lightly constructed and gain strength from buoyancy and incompressibility. The equivelent of a skyscraper could be just a bunch of netting will a balloon of gas or low density oil at the top. The problem wouldn't be keeping it up, but floating away.
Fire is not as important as we think. It's important to humans but that is because humans used fire to pre-digest foods and for light. In the sea, Pre-digestion could be done chemically (like a ceviche) or by enzymes borrowed from symbioses. Light would not be a big benefit because sight would be a secondary sense and in any case, could be generated by bioluminescent sources.
Neither is metal. Modern humans existed for 40,000 years at least before the first metals, and the civilizations of Meso-America built vast cities without using metals for anything but decoration. Metals are not necessary to technology. The primary use of metals was as wedges of different forms, e.g. knives, plows etc., but with slow motions like sawing, grinding, raking etc being the primary means of transferring energy, a wedge would not be quite as important. Hydraulic pressure could take the place of wedges when needed, especially if speed was not as important.
But, an aquatic species could develop metallurgy using electrochemistry which would be easier to develop in seawater, especially given they have electrical field senses to begin with. Magnesium is abundant in sea water and easy to extract with even primitive electrodes.
One could postulate a sentient species that has a anemone like symbiotic that radiates a powerful electrical detection field. The sentient starts out just anchoring the symbiotic around as a kind of early warning system. Selective breeding leads to stronger and strong field generation until they end up with something like an electric eel. (Which is how electric eels evolve.) Now they have a powerful, controllable and regenerative source of electricity. They would already be aware of calcium carbonate and silica precipitation by electrical fields so electrical metallurgy would be a short step.
They would also have an advantage in long distance communications. Sonics carry for hundreds of miles in the oceans and can carry multiple bands at the same time. Even at very primitive levels, they might coordinate millions of individuals over tens of thousands of hectares with the ease of which humans coordinate a small village.
I could imagine a civilization of highly cooperative, air breathing, squid-like critters, who used swarms to carry out manipulations and with strong division of labor e.g. that might have some dedicated to shuttling air bubbles, or a chemical oxygen store, to and from the surface, all coordinated over long distances and in large numbers by electrical fields and sonar.
Their primary structures would be made of carbonate and biosilicate foams, made buoyant with waste gases and strong by filling the cells with water or oil.
For mechanical energy, they could harness currents like a combination waterwheel, windmill.
Humans are so sight oriented that we have dull senses of smell, taste, hearing and touch compared even to other mammals. It takes us centuries to divine chemical compositions but a sentient species that evolved in salt water would be like living chem lab equipment by comparison. They would use those sense to develop a bioelectrical and enzyme based technology.
They would probably skip over iron and other ferric metals and instead go to aluminum and magnesium alloys, then perhaps various graphemes.
Their technology would emphasize skill, senses and complexity, all made possible by living in seawater, over velocity, shock and heat like most human technologies.
They might have trouble getting into to space because of their relatively low energy technology but then again they might try alternate technology like balloons that could rise to the edge of space and then form into sails to catch the solar winds and the planets magnetic fields. (There are similar designs tossed about here on earth but we haven't bothered thus far because we know a lot about fire.)
Once in space, they would have an easier time of it because living underwater is closer to microgravity than living in air.
So, yes it's fairly easy to postulate a plausible technological species once you stop seeing fire as something special and necessary. Once they have enough oxygen or other source of energy, the need to grow big brains for organization, manipulative organs and something to profitably manipulate, off they go.