The flight via YUL should be much more expensive and the extra customs visits make it a hasle - were you awake when you made this decision?
As a matter of fact, I was awake, and it's a good thing I was. By some fluke, I hit upon a short-lived fare that was $200 cheaper than anything I had been seeing at BTV, while offering me a non-stop evening flight on the way out Thursday and letting me avoid a red-eye on the way back. The scheduling was perfect and the fare was well under what I initially though I would have to pay to take this trip, so agreeing to make the drive up to YUL and deal with the customs clearances was a no-brainer.