Normal driving time from downtown YOW to YUL is 1.45 to 2hrs. (It can be done in 1.5 hrs... in the middle of the night, by someone with a death wish.) On a Friday afternoon, you can expect it to take a bit longer to get out of downtown YOW, and perhaps a bit longer to get into YUL, but I can't imagine it taking longer than 2.5 hrs in the absolute worst case scenario which puts you at YUL comfortably before your flight.
Tricks? OLCI and have your US Declaration filled out ahead of time.
There is no longer a gas station on the YUL campus, so you will need to fill up your rental before you get there. My usual route is 417E => 40E => Sources Blvd or St Jean Blvd. (gas statiosn on both of these) => 20E => YUL.
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