Ah, perfect! I had been looking for it tied to a device, not the account itself.
Alexa in Canada - when I tried adding the number through the app it told me that the number was already connected to another account (my Canadian account), and wouldn't assign it again. I'll see if adding it through the website will allow the same number in both accounts.
Yup, adding it through the website as opposed to through the app allows the same number to appear in both accounts. Woohoo, thanks for the help!