I crossed at the Detroit-Windsor tunnel last week, with another musician friend, and wasn't asked for id on either side. It's hard to say what they'll ask or want to see. For now, a photo id (like a driver's license) and a proof of citizenship (like a voter registration card) might be enough. We were at the Kildare House session, and we told the customs guy that. All he asked was whether we were bringing anything back.