Allan, try this trick: when prompted for a US ZIP Code, enter the three numeric digits from your Canadian Postal Code, followed by two zeros.
Donna, for your information, using a credit card is safer than using a debit card for retail transactions (like getting gas).
With a debit card, a person's live, available bank balance is reduced in case of a hold, an error, a malfunction, or unauthorized use of the card. This can leave insufficient funds for checks and scheduled transfers, producing a cascade of fees. It can take weeks for the bank to reverse inappropriate debit card transactions. Even if the bank also reverses its own fees (overdraft, NSF, etc.), payees have no reason to reverse their fees (late payment, returned item, etc.).
When something goes wrong with a credit card, bank balances are not affected.
Moreover, for Americans, the "special rule for credit card purchases" applies only to credit cards. The special rule is the basis of the right not to pay for goods and services that are unsatisfactory or were not provided. Although some debit card issuers extend similar protections to debit cards, they do so on a voluntary basis.