Did you make a mistake at some point when you created your Square Enix account? During registration you're given the option to choose a country and choosing Canada gives you the option of choosing a province, city and postal code. If you chose US for some reason at that point then you wont be able to register a Canadian credit card. Do you have a province and postal code listed in your square enix account information? If not you'll need to get on with chat support since you can't change your country by yourself.