The cellular functionality wont work most likely. Even if someone tells you their got their US specific model working it would be useless to you unless you are in the same country and same cellular provider. Ultimately its up to provider. This page lists model numbers that cellular providers support in different countries https://www.apple.com/watch/cellular/
Cellular calls and data won't work outside the original territory for the Watch, but emergency calls and notifications for things like fall detection will work in most countries even if the watch is never activated on a cellular account.