Yes, you literally tell the Canadian border agents your purpose for coming to Canada is to fly out from Pearson (or Trudeau, or whatever airport). For people in Northern VT Trudeau (YUL) is closer than Boston and has nonstops to Europe so this was a thing before the #TSA mess.
@sfergs_ I never thought that was a thing people could just do...but I can't see why not. So when they cross into Canada, they just straight up tell the border guards "yeah, I'm going to Pearson to catch a flight" in a foreign country using my American passport to go to another country??
