Don't you have a friend or relative in the US whose address you can use?
Or a way to buy gift cards at B&N and send them to yourself and then add them to your account?
I purchased a Nook based on advice that Canadian accounts worked as well as US.
You were misinformed. Canada forbids brick-and-mortar booksellers such as B&N from doing business in Canada. You can complain to your MP about the Investment Canada Act.
I have sent you a Private Message (the small white envelope on top of the page).
If you have a NOOK and you live in Canada, you can purchase books for it from Chapters/Indigo via Kobo (kobobooks.com).
I bought several gift cards last time I travelled to the US. No tax, no duty, not worries.