It looks like the US site has now activated shipping to Canada. Of course, unlike bananarepublic.ca, you'll have to pay duty. For example, the faux wrap dress on Banana Republic's Canadian site is selling for $124, while the US site is selling it for $104.64. However, since there is no duty or shipping on th Canadian site, the total cost for a bananarepublic.ca purchase is $140 (or $149.16 if you want it quicker) if you're buying from Ontario (13% tax here). If you purchase from the US site, the total cost is $165.44.
I hope the Canadian site will eventually add petite/extended sizes. After all, there's more than a $25 difference. I guess if you're really desparate for certain items or sizes, you might just bite the bullet and buy from the US site....