Originally Posted by MapleLeaf
Technically when you pass through DHS in Canada at an airport, you have entered US Soil. If you want to go back outside the secure area, you have to pass through Canada Customs/Immigration as you "have been out of the country"
I don't believe this is correct. In the event of a cancelled flight or other reason to not take your flight, you are free to leave back through the US Immigration hall and go back into the terminal. I have done it many times.
Employees who work in the terminal pass back and forth without being inspected by either US or Canadian officials.
Also, the sterile area after pre-clearence is still considered Canadian soil - the US government has no authority there...actually, they don't even have authority in the Immigration or Customs area - if Immigration wants to bar you, or Customs finds something illegal in your luggage, they have to summon the Canadian police to intervene.