I didn't think you could book it in anything BUT the currency of your credit card.

For years I have been booking tickets (WITH HASSLE) at AA.com, and always had to make sure I checked on the system to change its ticketing location to CANADA. If I didn't the payment would never be processed. I think it verified with a ZIP code or something.

Anyhow over the years I have just made sure to change the country link in the top right corner of AA.com before I even start the booking process.