Originally Posted by Microwave

You beat me to it, though as far as I know both the first line of the address and the Zip code are validated, so a random Zip code would fail. To put a Canadian postal code into a US Zip code field, one would drop the letters completely, then add as many zeroes as needed at the end to make a 5-digit number. So, say your postal code was K1A 0A1, you'd put 10100 as the Zip code.