I live in the UK and on most comics it says "£3 USA £4.50 Canada" I have always wondered why, Is it because of Tax or shipping???
As far as I know it is because the Canadian dollar was much lower in the past. So basically the comic would coast the same and it wouldn't pay off to buy comics in Canada (economic protectionism really). Today where the Canadian dollar is about the same level as the US it doesn't real make that much sense. It is not limited to comics. It is also includes books and other products that has a define price tag on it.
The Canadian dollar is worth a little less than the American dollar, which with today's economy I'm suddenlt very sad for Canada
It doesn't just apply for comic books though. I think it applies to everything Canadians buy from/in the United States, but I could be mistaken.