I believe that option is only for adding another e-mail account to an already existing full .Mac account for an additional $15 CAD. With the U.S. plan you can add another e-mail account to your full .Mac account for something like $10 USD. So that's probably what you're looking for. But since it sounds like you don't already have a .Mac account, you won't be able to get it (and it would be silly since you'd have to buy .Mac and then pay the $15 CAD to get the other e-mail account).