If you are a canadian citizen, you can not join the service unless you forfeit your canadian citizenship.

As for your query itself. You can do it. Every subject follows the same pattern, there are important topics, prepare notes for them, memorize your notes, and write down the answer when it comes in the exam. That's all there is to it.

The essay requires some guidance from Pakistani teachers in terms of what kind of structure and approach you should have, but even that is all very common sense.