How to make an earthquake
Earthquakes are massive. They're possibly the largest-energy event that humans experience regularly, rivaled only by hurricanes. The Earth does a lot of this energy creation for us and when earthquakes happen, it's the result of that energy being released. Fortunately, earthquakes are essentially limited to fault areas- the boundaries on the edges of plates where they rub up against each other, creating transform, convergent, or divergent plate boundaries. The center of tectonic plates is relatively stable, so I hope your enemies live near a large fault system or we're going to have a much harder time.
As a simple model, imagine two elastic piece of plastic pressed against each other being pulled in opposite directions. Eventually, the pulling force overcomes the force of static friction, and the plastic slips. Thus, there are two places we can affect this process: decrease the frictional force or increase the "pull" force.
Decreasing the frictional force:
This is definitely the easiest way of solving this problem, because humanity is already doing it. Fracking-induced tremors are a hot-button issue in the US right now, but the science is pretty well established. Ellsworth (2013, in Science) reviewed a lot of the literature and found that "injection-induced earthquakes [...] clearly contribute to seismic hazard." He references a magnitude 5.6 earthquake in Oklahoma in 2011 that was tied to local fracking behavior. Interestingly, the use of fracking may not only directly cause earthquakes, but can also make them more likely to be triggered by other earthquakes. In this case, the fault is weakened just enough to make it susceptible to triggering when seismic waves pass through.
The mechanism behind this is a bit more complicated than our simple model of elastic plastic, but intuitively is the same. By injecting fluid in between the two plates, they slip more easily and the tension in those plates is released. In real life, the introduction of fluid and changes in pressure weaken a preexisting fault and allow movement.
To use this mechanism to attack another country is less a question of military might and more a matter of politics. Introduce your frenemies in the other country to fracking techniques and watch their country crumble. (Due to earthquakes, of course, not the desperate and all-consuming realization that one lives above an easily removable energy resource that everyone in the world would suddenly be interested in.)
If you're desperate enough to need such an earthquake now, you might be tempted to use the biggest bombs you have. PLEASE DO NOT TRY THIS. The USGS has considered this possibility and is rather dismissive of it. They detail several tests and the bomb signature was always greater than the seismic signature, and even when detonated on a seismically active area such as the Aleutian Islands it failed to produce an earthquake. (Of course, that's conveniently also what the government wants you to think...) One of the most persuasive arguments they use is to point out that the Moon exerts tidal forces every day ~40x larger than the Tsar Bomba. Although I don't believe Canada maintains any nuclear weapons, your country might still have a pretty big bomb, but it won't be big enough- any fault that could be triggered by a bomb would already have been triggered by the tidal forces of the Moon.
Increasing the pull force
Well, that might have been a fairly dissatisfying answer but it doesn't get much better. Despite it's reputation for delicacy, the Earth is a fairly stable place. The source of plate movement was hotly debated for a while, but has been pretty well resolved mostly in favor of slab pull. Slab pull is the result of oceanic plates cooling after formation, causing a reduction in volume and an increase in density with age. Eventually, they become more dense than the mantle material and sink.
If you've dropped a cookie in a glass of milk, you have a good idea how this works- the cookie starts out more buoyant than the milk and floats on the surface, giving you hope that it can be rescued. By the time you've returned with a fork, however, the air pockets have been replaced with milk and sadness, the cookie as a whole is now more dense than the milk, and it sinks to the bottom.
I personally have no idea how we could affect this process. It's density driven and takes literally millions of years, so there's not a whole lot humans can do on this end to force earthquakes to happen.
If your enemy nation is on a coast, it may be easier to cause a tsunami than an earthquake. Michael Crichton's book State of Fear has a group use
explosives to trigger the collapse of an Antarctic ice shelf
which would cause a fairly sizable tsunami if nearby.