You can now pre-order an iPad through Apple Canada:

Unless you plan on watching a lot of movies, you don't really need a large size.  From our experience here at the office (my co-worker got one sent up from the states) it's not like an iPod/iPhone where you want a lot of your music with you.  It's unlikely that you're going to go jogging with your iPad on an armband.  The 16GB will be plenty for most people I'd imagine.