> Because you can't exactly sneak on/off of an international airplane.

I'm actually pretty curious about this. You can't easily sneak on/off a commercial international airplane, but that's because they've got the gates set up in the airport to funnel you through a specific path that leads to customs. Showing up on an international charter or GA flight seems squishier. http://www.canada.eaachapter.org/FLYING%20TO%20and%20FROM%20... The process seems to be that you schedule an ETA, taxi to a CBP station and wait there until a CBP officer arrives.

On the other side of it, it looks like CANPASS would let you land in Canada even if the CBSA station is closed...