NOTE: I apologise in advance for this. I enjoyed myself so much I got carried away. TLDR: No, I think that they will not be able to share a world in peace.
These humans are a giant threat to Giant Society
These small creatures are an immediate threat to giant society! Do not trust them!
The humans are cunning and many giants do not trust them! The humans will quickly learn how to exploit their protectors' stupidity. They will prove their intellect by creating things no giant has ever done, and quickly rise to be superior in literature, music, arts, architecture, design, language, and agriculture.
The humans say they remember things from where they came from; they begin to talk about "Machinery" and "Steam Power".
They will introduce new farming methods such as crop rotation, and the giants will hail them for their "revolutionary" ideas on steam power. Machinery will quickly develop, leading to factories and a busy industry, all created by these humans.
Giants, unable to comprehend how any of it works, will simply accept their role as factory workers or heavy lifters within this newfangled "modern age".
The elder giants are now worried. Despite all our notions of "Innovation" and "Discovery", the majority often fear new things (especially the older generations). Those elders who have power within the giant society do not trust the humans! They call for the giants to not work for them. Meanwhile, the younger giants are gaining money, resources, and all sorts of new goodies from the results of the humans' creations. They side with the humans, their saviours.
Giant society is being split into two and there is a lot of unease among the people.
The giants know that they are stronger than the humans, despite their outward appearance of being able to manipulate the land. The elders tell their people about how the factories are putting smoke into the air, and forests are retreating and being burnt down to fuel these places of hard labour, where the human owners reap the greatest rewards and give the scraps to the giant workers.
Some giants, seeking material wealth or power will side with the humans, revelling in their creations such as "Trains", "Cannons", and the recently created "Automobile". Black powder, used in the mines for breaking stones that even the giants cannot crack, is used in their new "Musket" to hit things from far away!
The elder giants mass a group who say that they should never have taken the humans into their world, for they have brought destruction of the trees and pollution of the air. They use their dark powers to make their automobiles move, and since none of the giants know how they work they begin to beleive them.
They seek to destroy the humans' creations.
What is it good for?
They say that the giants who side with the humans are treacherous, greedy, and power-driven. The humans do not fear the giants though, since they can hit from further distances with weapons far outweighing the giants' bows and ballistae. The giants specialise in melee combat, but the humans have surpassed that level. After the first strike, the elders declare "war". The humans, on the other hand, declare "extermination".
The humans have faster boats, and their navies can destroy towns and villages on the coast with their explosives. They can take down stone outposts that have stood for years with their iron shells.
Their "Automobiles" can outrun any giant or their mount, without halting. They can carry heavy guns, or food supplies, or anything they want.
The giants never get close enough to use their sword, axe, and hammer skills. The giant archers have better luck, but do nowhere near as much damage.
Some giants who joined the humans see the destruction of their people and plead for mercy. Some even rebel. The humans were clever enough to see this coming though, and have systems in place to deal with them.
Destruction continues until the giants surrender. The humans survey their work, and what is left?
The humans have brought invention and intellect to the giants' world but it came with a price. The giant clans had always fought amongst themselves, but their forms of combat never left the battlefield. The price for new inventions is that they can cause more destruction. The humans' inventions have lain waste to everything, simply to defend themselves.
Giant populations are down, and human populations have grown. The giants go into hiding in the mountains and the humans spread over time to claim most of the lands. The giants fade in the humans' memory. For the giants, they remember. They tell stories of the destruction of their world. They cannot leave their harsh climates without risking discovery. They live in fear, but for generations to come, they will not know what that fear is.
Perhaps one day they will resurface in desperation to find food. They will go forth in their small numbers to find an advanced race, with "Roads" and "Computers" and "Aeroplanes", and will search for jobs in order to feed their families.