I'm an Australian living in a town with a pretty high level of immigrants, including a lot of Americans and Canadians, and I can't tell the difference between an American and a Canadian at all. I'm not entirely convinced the difference between a Canadian and an American would be any bigger than the difference between Texans and Californians, for example.
The difference between a Canadian and an American is about the same as the difference between a Kiwi and an Aussie. Likewise, the difference between a Texan and a Californian is similar to the difference between someone from Geelong and someone from Sydney.
