Job Search - Adding the Country Field

We are preparing to launch in the US. We have created a US Career Centre Page. I'd like to add "Country" as one of the search criteria, but I don't see that as an option for Search Criteria. Am I missing something? What field would you recommend that I use so that Canadian and US candidates can easily target their Country and then their Province/State when searching for reqs without having to select from them all? Region?