Because it’s just for you Yankees, Amazon.ca is for us Canucks.
I almost lost a pre paid Visa on Amazon.com had the order all filled out and it wouldn’t accept my Canadian address and I couldn’t the card back, but I beat em I just sent my American Uncle an early Christmas present.
I would suggest loading funds into a PayPal “bank” (basically, just a PayPal account), which can accept funds from multiple sources, and then use that single PayPal account to pay Amazon.