Yul is my home airport and I just wanted to add my two cents.

Transiting through YUL you will go up some stairs along a corridor and at CBSA you will be doors that open directly into the International area

The MLL International is a good lounge better than any UC but not on par with the Polaris Lounge.

If you have Amex Platinum you can access the AF lounge. Decent lounge with a great buffet, real champagne and showers. May or may not be crowded.

As far as LAX would United make an exception for PL access acca through long-haul ticket that is sold as UA flights on UA ticket stock?

If not you can walk airside to the International terminal. The Star lounge is great an so is the Centurion Lounge.

Safe travels.