(Where "American" is used in the normal way to mean a US citizen, rather than a resident of the American Continent.)
An American friend of mine, now living in the UK has described
how, in polite London society, she is always asked if she is a Canadian,
never if she is American. She supposes that this is to avoid causing
offence, rather than because she seems distinctly Canadian (she does not). There seems to be an assumption than it
is less insulting (perhaps even
complimentary) for an American to be mistaken for a Canadian than for a
Canadian to be mistaken for an American.