I'm bold, but not to the point if what OP seems to want:

1) represent to US CBP that they are passing the pre clearance border to fly from Canada to the US

2) meet with officers from both US and Canada

3) cancel the ticket and suddenly need to ask for a security escort back through Canadian immigration.

AC has booted people for less (visiting a lounge allegedly not intending to fly, then needing an escort). That case didn't seem to even have false declararion to US or Canadian officers