As a Canadian, getting offended at American being used to describe people from the USA strikes me as someone who wants to be offended. It’s totally unambiguous in (almost) any company, it’s not “stealing” anyone’s identity, and there’s no good substitute.
I suspect (and dearly hope) that your sample group was loaded high in those suffering from offensensitivity. After all, the Canadian identity is best expressed in a feeling of smug, but silent (very important!) superiority over our neighbours to the south, not in lecturing them.
