That's because Canada doesn't have the buying power as US consumers. So they can get away with it. But in this instance the government is dictated the minimum price you can charge for the product.
I dispute this. Given free trade, why should something that sells at Home Depot in Toronto cost more than something that sells at the Home Depot in Buffalo? Why can I drive an hour south of Ottawa, cross the border, and buy something from the stores in Ogdensburg, - which is a burg - and it's cheaper than in Ottawa?