The simple answer is "none." There's no more difference between "U.S." and "Canadian" than there is between different regions within the United States. I am not usually aware that someone is Canadian just from listening to their speech. The only exception is that some? all? Canadians pronounce the "ou" diphthong in words like "out" just a little differently. It's NOT "oot" but it is a little bit of a shift in that direction. If someone talks about "a can of pop" I might ask if they're from Michigan. If someone says "that needs fixed" I might ask if they're from Pennsylvania. If someone says "oot" I might ask if they're Canadian. Peter Jennings was a famous news anchor on the U.S. network ABC News. Until he died and they ran the obituary I was completely unaware that he was Canadian.

I am Canadian and I feel that it is mostly the same. We do have a little more British influence so our spelling is sometimes different. There are a few uniquely Canadian words but 99% is the same. It mostly comes down to accents. Although most of the US and Canada would be very similar, people from Eastern Canada have a thick accent (that even other Canadians find funny). Similarly, the US has different regions with different accents (eg. Boston vs L.A. vs Texas).

There is not much of a difference.. They sound almost the same. the US is really big and they have their own accent in different states. So I wou say that Canada is like another a different state that is part of the U.S.