Sport pilot - International?

How is this (Sport pilot) going to work when you cross a border? I'm
thinking specifically of the U.S./Canada line, but also U.S./Mexico.

Currently (I'm told), when you re-enter the U.S. coming from Canada, the
U.S. Customs inspector asks you to show your medical certificate. If you are
flying under the upcoming Sport Aircraft provisions, will they (Customs)
allow you to proceed with a driver's license as proof of certification?

Rich "Please let me back in my own country" S.