Wow, amazing to me that you've never visited Canada since you spent your whole life a stone's throw from the border. When I was in NY I used to go over quite often. It's a beautiful country and the people are usually awesome (except for that one time in Montreal when I met some of the rudest people on the planet). The beer's not half bad either. And you can't beat that tropical Canadian winter, eh?
I've always thought the Midwestern accent was similar to the Canadian accent so it's not surprising to me that people mistake you for that. Lots of cultural similarities unsurprisingly. It is an imaginary line on a map after all.
Alas, by the time I was in any position to travel on my own, the government gestapo started demanding, "papers please!" And I never bought the right permission slips.
Showing my age here. We used to go over to drink when I turned nineteen. The Canadians were more thorough when we would go over the border. They actually asked us "citizenship?" The US border guards would just wave us past, sometimes laughing at the guy in the back seat with the spins. Oh how things have changed.