Do as it directs, go to the URL and follow the instructions:
www.apple.com/support/itunes/ww/ --> https://support.apple.com/country-selector/itunes > select your country > Contact Support > Contact iTunes Store Support > Purchases, Billing & Redemption
That said, I suspect the problem will be when you set up an Apple ID or change an ID to a new country you will be required to enter a valid form of payment for that ID. Some here will say that for the USA this has to be a card from a USA bank, but nowhere does Apple actually say that (in fact in one place it intimates you can use payment forms from other countries -- "If you're outside of the United States, you might need to contact your financial institution to allow international purchases." ). Nevertheless, it could be true or at least be indirectly enforced by you finding that you cannot enter a Canadian address for your card in the US form for entering an Apple ID payment method
Note in general that using the stores in another country is against the terms and conditions for use of the media services. https://www.apple.com/legal/internet-services/itunes/us/terms.html - May 13, 2019 "Our Services are available for your use in your country of residence (“Home Country”).".
So basically your friend was nice in sending you a gift but you cannot use it. Unfortunately if you have now redeemed it this sets up elements of complexity. See if your friend can get the card refunded. If not, she will have to take control of the Apple ID you set up, use that to spend the money and then set up Family Sharing with her/himself so she/he can get access to the items from her/his regular account.