Shipping restrictions

I cant seem to find how to do this - I have some products in the database, that I dont want to be shipped out of the USA because they are coming from a supplier or myself - how do I prevent this from happening - I suspect I cant stop them from adding it to the cart - especially if they are doing it as guest - but when they do enter shipping address if they have something that I defined as restricted, warn them or something…

any ideas - I suspect this is something happening presently?

I guess I should add this

I have a shipping method presently that has nothing defined for Canada and default countries - so just US states - and what I get when I estimate shippign with a Canadian address is the no shipping methods defined - where ideally I would like to say, “please remove” or “unavailable to your country” etc… I know I can change the language string - but then it would need to be generic - any thoughts?