I'd go for more than the three gears. You could well discover new trails at some point where you'll want more than that. I'm not up on the movements of the Canadian Dollar, but I'd imagine it's reasonably close to the Australian dollar (I think we're about 75 US cents right now), so that shouldn't break your budget.

Front suspension is good, but rear suspension might be a little redundant. As far as sizing goes, you'll probably be looking for something in the 18"-20" range. However, a lot depends on the length of your legs and so on.