That's annoying. Avis obviously doesn't want to move vehicles from downtown to YUL so they are blocking those right now. That may change closer to the pickup date. Or it may not. Here's what we would do:

1. Keep checking as availability can open up. If you want, you can track your original reservation with AutoSlash and we can set the price to 9999 so you get notified of any availability.

2. Book a new round-trip rental at a downtown location for the pickup and return times you originally planned. When you pick up downtown, ask at the rental counter if they adjust the return to the airport, and if so, how much that would be.

3. If the counter can't do it, or it's too expensive, call Avis' rental extension line the day before you plan to return and ask the same thing.

4. Failing all of the above, you can always fall back to returning downtown and then taking a cab/Uber to the airport, but we don't think it will come to that.

Hope this helps!