In Canada postal codes are unique to an address. So unless you live in an apartment building, it *is* your address.
Using credit cards with an international address in the US can be a pain for some things. In my experience, for example, you cannot use pay at the pump for gas, because the system doesn't recognize non US zip codes, and that's what's used for identification.
Mind you, if you have a US credit card without a chip (I think most don't, right?), you may be out of luck travelling when travelling abroad because you can't enter a PIN, which is the security screening for those cards.
I've had problems using international cards for buying stuff on line. A lot of sites aren't set up for international addresses, and sometimes it's physically impossible to enter my address, or I can't make it match the way it's reading the address to check the credit card payment, or it simply doesn't fit in the amount of space provided.