When entering an address for a contact/customer in NS, if the country is US and we enter a ZIP code, the city/state autopopulates. Is this a built-in NetSuite thing, and if so, is it possible to make this work for Canadian Postal Codes?

Yes it's a built-in NetSuite thing. It's not a switch that gets flipped on for it to do that; it's just native to the system and is automatically on. For that reason, if it doesn't already work for Canadian post codes, I'm guessing there's not a way to make it work. At least not an easy one.

grumble grumble

😄 Hey I could be wrong. Can see if anyone else knows differently. Maybe there's a way to call that service, though if it was there and available for Canada, I would think they would have just hooked it up so it works the same.

Even if the service can provide US postal code lookup doesn't mean it will support Canadian postal codes, as they come from two different sources of data. There are a number of third party services that do this, like Precisely, and you can make calls to their API to get the reverse lookup: https://developer.precisely.com/apis/addressverification -> GetCityStateProvince supports Canadian and U.S. lookup from postal code