The issue resolves itself when you are both geographically in the country and admitted by immigration. When travelling from YYZ to the U.S., both countries for immigration purposes consider me in the U.S.A. once I've gone through pre-clearance. If I change my mind or the flight is cancelled I have to go through Canadian immigration to be readmitted. For non-immigration purposes however I am still in Canada so should I commit a crime on the airside I will be charged and prosecuted by Canadian authorities.