Amazon app store is not available in Canada,
However, if you put a US address in your profile and delete all canadian addresses, you will be cloned as a US customer and therefore able to download apps.
You can use Amazon gift cards or a credit card with a us address.

I bought 2 Kindle fire, one for me and the other as a present, looks like I'm going to sell the other one. Any takers? $240, what it cost me to land it here.