Canada is the only foreign country I’ve visited where you not only can claim a tax refund on goods purchased over a certain amount but you also get your GST tax (6% as of July 1, 2006) back on your short term accomodations. Do the following:
Make sure you get a receipt from your hotel stating that the GST was charged and clearly states the number of nights and what the cost of the room is, you do not get a refund on room service or other additional services.
If you are just claiming a refund on your hotel, you do not need to get the paperwork stamped at customs, if you are also claiming a refund on the tax on goods, you do have to get it stamped at customs before you leave.
Someone on another forum mentioned that you should not use the "Tax Refund" brochures with brightly colored covers showing national flags that you find at many hotels, they apparently keep 10% of your refund as a fee in addition to service fees and a currency conversion fee. Instead, look for the "Tax Refund for Visitors to Canada" Form RC4031 published by Canada Customs and Revenue Agency which is white and red or you can download it from the Canadian Customs website
One word of warning, if you book with a company like Priceline or Orbitz and you do not get an itemization of the taxes, you may not be able to claim the tax refund. If you save enough by booking with them, it shouldn’t be a factor as the tax is only 6%. I was able to get a refund on the one night booked through Priceline when I was staying in Montreal, I went ahead and submitted my receipt and showed my calculation of the tax at 6% on the room and they did refund it. It took about a month to receive my refund check, if possible they issue it in the currency of the country where they are sending the check.