I've never heard "Canadian" used in that manner, so I would say that while this man seems to have adopted it to be used as a racial slur, it is not something that is going on in the entire south. To my knowledge, most Americans do not have much of an opinion at all about Canadians. You guys are close enough neighbors that we don't view you much differently from ourselves.

Also, there are still some bigoted idiots here as there are elsewhere, but the rest of us do not like them and do not take them seriously.