"It's that napkin/serviette, toilet/washroom/loo, trash/garbage type dichotomy, where I can't see a difference, but are apparently class indicators as well as signs of American influence, that I feel I'll never get hold of."

I think that's a Canadian thing. English Canadian culture is to a large extent a blend of the American and British (although perhaps moreso 20+ years ago than now). As a result we tend to be comfortable using expressions such as those you cite above interchangeably.