We have a credit card issued by RBC Bank Georgia (an American Bank owned by RBC Canada) and use it with our USA address. We also have a US dollar credit card (issued by a Canadian Bank, BMO) and also use it with our USA address. The Zip code pretty much always works at the pumps. Only exception we’ve encountered is the BMO card consistently won’t work at one particular station we go to every year in Florida. I’m guessing that station’s pumps are programmed to reject non-USA Bank issued cards (they can tell from the card number). The USA RBC card works fine there.
A few years back we tried a number of different work-arounds (including the postal code thing) with our CDN cards without much success but decided last year to try again. I was quite surprised to find that the postal code trick now worked more frequently, but not always.
Last time I looked at this, debit cards (with PIN) from some (not all) Canadian Banks could be used at some (not all) US gas stations. However, many advise against using a debit card. More protection with a credit card.
CDN debit cards in USA