British shows go over better in Canada than they do in the States - that's been proven quite a few times. The reverse is true too - Canadian shows like Trailer Park Boys are being considered for British release, but most journalists think it wouldn't go over well in the States. I'm not sure if it is that Canadians have an easier time with British accents, but I don't think the accent is a major issue over here.
There have been a few British hits in Canada that I can think of: Monty Python (the biggest and greatest), Faulty Towers, The Office, and Black Adder. It's not like they are enormously successful, but they have pretty decent fan bases. All but The Office are shown regularily on TV over here (The Office is available on DVD at just about any electronics store though).
I'd say the biggest issue is British slang. There is quite a bit of it that people in Canada have no clue about at all. I've been thinking of making a "Translate this British slang into English for me" thread for us North Americans who are lost with some of the sayings in Top Gear.
I think that Top Gear would go over quite well over here. Quite a few people I know watch Fifth Gear on SpeedChannel and really like it. I'd be really interested to know the American\Canadian ratings of Fifth Gear on Speed Channel, but I think Top Gear would do well over here.
(I'm talking about widespread airings of full episodes here - we already get the crappy BBC World versions on the BBC World channel - it's a really obscure channel and hardly anyone watches it)