And to think I thought they were just being polite

I've lived in London for over 15 years now and, although my accent was never terribly strong, it has softened considerably over the years. Nonetheless I have not acquired a south London accent and it is fairly clear to most Brits, if not most Americans, that I am from North America. It is not uncommon for me to get the "are you Canadian?" question when meeting new people. I always thought it was because people were uncertain as to whether I am a Yank or a Canuck and, assuming that a Yank would less likely to be insulted by being mistaken for a Canuck than the reverse, that they were simply erring on the side of caution. I am no longer certain that that is the case.