The postal code should do it, but if your seller is a tad paranoid, he may want your entire address because: paranoid.
If he can't accept your city* and postal code as enough information he is either deeply nervous or really doesn't know what he is doing.
Oh. He may also want to screen out buyers with post office boxes. This is good for you, because it also means he is planning to ship by a courier like UPS, which cannot deliver to PO boxes. Since those couriers charge $25 or more as customs brokerage fees, you will not be happy when the man in brown demands large lumps of cash on your doorstep to hand over your purchase.
*Because the postal code really doesn't mean much to foreigners. Or even to Canadians. Do you know how to spot a rural address from its postal code?