Welcome to the group and excellent question my fellow Canadian. As tempting it would be to go out and buy a U/W camera for your trip, my first recommendation is to take an Open Water course, and then get out diving here in Canada before your trip. It's highly important you develop good buoyancy skills. Not just for getting that nice sharp photo, but for the safety of the reef. Trust me, the last thing you want to do as a diver is to destroy the environment that you enjoy seeing so much. As an underwater photographer, it is so easy to get tunnel vision and lose all sight of what you are doing when they focusing on The Shot. This why one member suggested being aware of the time, air consumption, and depth while you are diving.
Feel free to message me if you need any help in finding a dive shop here in Canada.