You can tell a Canadian accent typically if they sound mildly retarded. People from the South tend to sound mildly retarded too, but they're easy enough to distinguish from the Canadians. Having grown up in northern Minnesota, I guess the Minnesotan accent does sound a bit dumb, not as dumb as Canada though. Really, it's more grating than anything.
The Simpsons said:Bart: So, what are you in for?
Gordy: I moved here from Canada, and they think I'm slow, eh?
Also, if you ever see Income Properties on HGTV, the host, Scott McGillivray is pretty obviously Canadian sounding. No American speaks like that. For the love of God, he pronounces progress as pro-gress (emphasis on the 'pro', eep!) instead of praw-gress.
Wow have you ever talked to a Canadian, I would respond with mean words but i will try and stay above that. Just really insulting. Any other nationalities you want insult and call mildly retarded or is Canadian and Scottish the only ones? Funny we are in a Star Trek forum, here we are fans of a show that encourages us to "PRO -gress" toward a humanity in harmony and unity and we have people saying things like this.