In Canada it's different because only two provinces (Ontario and Quebec) even allow tipped employees to be paid less than minimum wage and even in those two cases the minimum wages of tipped employees is very close to the minimum wage of untipped employees so they don't have to rely on tipping as much.
With that being said I noticed the general consenses in the U.S. is that Canadians are bad tippers so maybe that might be part of the reason. I know when I'm in the U.S. though I tip the same as I do in Canada (from 20%-40% depending on service) but some Canadians might not be aware that U.S. employers are allowed to pay their waiters/waitresses so low.
ps. I'm considered a generous tipper in Canada...
*Edit: Oops I also meant to say that I think Entroper is right and 15% is the standard.
