Anyone knows if they've announced plans to do that?
In Canada no bookseller can be majority owned by a foreign company, (they can only own something like 25%, it's seriously screwed up). Amazon doesn't operate foreign subsidiaries and so it can't legally own property in Canada for it's business. Canada Post however essentially gave Amazon a permanent lease of one of their large distribution warehouses in Mississauga right on the Canada Post's own central distribution point for all Ontario post and the central hub for all post travelling through Canada.
Indigo/Chapters/Coles (the same company) cried foul in court and to the government, however the Judge ruled (IIRC) that as Amazon didn't own any property in Canada they were exempt from the ownership laws. Obviously when the laws were originally set in place they didn't realise how easy it would be for a company to operate without its own property.
I doubt Amazon.ca will come to mirror the US site any time soon. They're in a tough situation and until the laws change, they likely can't afford to jeopardise their position.
I don't fare well as I used amazon for nearly everything while in the UK, but now in Canada I'm stuck with CrapBuy and Shit-Mart who sell everything at hiked prices.