(Jokes aside, they are. I've been in pools with money in the pocket of my trunks at a water park, and the money was perfectly fine and they still accepted it when it was wet)
US dollars are partially fabric, so they are waterproof, in the fact that they can get wet and then dry, but they will get wet. Canadian cash is basically like a plastic now, so it won't absorb any water. I send American notes through the wash all the time (when I leave them in my pockets).
Oh Canada, we stand on guard for thee.
No, I will not at all sit in a corner and sniff-n-scratch money