Well I just received my Collector's Edition from Gamestop.com [via UPS, shipped to Canada] and, surprisingly, I only had to pay the GST for it [which was only a little over $5].
Yeah, it's unfortunate that I had to pay the shipping cost + GST for an additional copy that I have no need for [and will be promptly returned to the store for a refund], but at least it's less of a burden than having to return it to Gamestop.com and wait for the credit to be applied.
If I can't return the US copy to a Canadian store [for whatever reason], I'll simply keep the US copy and return the Canadian one. I should, hopefully, be receiving the EBGames.ca CE soon [it's been on the truck for "delivery" since 8AM this morning -_-].