Hudson Bay is not counted, but the great lakes are.
It's not the ocean that's being counted. It's the Artic Islands.
Yes it is, but you have to include all of those islands, in particular Baffin island. If you just look at the contiguous land masses, the US is bigger, which is why it looks bigger on this projection. If you dragged all those islands together into Canada, then Canada would look slightly bigger, because it is slightly bigger.
Canada (without the various arctic islands) is considerably smaller than the contiguous (sans Alaska and Hawaii) US.