Meh, I don't find any stereotype annoying. Most Canadians don't care much either. We are well aware of how we're portrayed in American TV and movies because 95% of what we watch is produced in America. Canada doesn't have a very big entertainment scene of our own.
The Rimmel commercial is English supermodel Kate Moss, and she happens to have a gap tooth. I don't think anything else of it. It's "the London look" and she was actually born in the London area. If it was an American model with a gap, I might find that questionable. Otherwise, no. It's simple marketing - they used a model from London for a London-esque campaign. Yes though, I agree the British get stereotyped for bad teeth which isn't always true.
As for Canadian's drinking maple syrup like alcohol... We like maple syrup and we like alcohol, so I don't see the problem. xD Nah, we Canadians like to make fun of ourselves from time to time. As long as it's all in good fun, we have a good laugh at it too. I find Canadian jokes hilarious. People who can't laugh at themselves from time to time are too serious.
As for how we stereotype America. The biggest one is that they don't know anything about the rest of the world.