I can definitely clarify this for you as I know how important it is to have a full understanding of the products and services you're using. QuickBooks Online Payments in Canada does not process Amex cards. At this time, it's only Canadian Mastercard, Visa, and Discover credit cards that are accepted through the program. You can also use Apple Pay in conjunction with one of these three cards.
We know many customers are eager to be able to process more cards than currently available and I want to assure you the product development team is taking this into consideration. Our goal is always to do what we can to enhance what QuickBooks Online and its related services can do for our customers.
I encourage you to submit feedback about this through the Feedback tool in your Quickbooks Online account's Gear icon. It's a great way to share your voice and requests directly with the product development team.
Let me know if there's anything else I can do for you!