I've unfortunately become an expert at this run over the past couple years and the lack of direct YUL-YEG flights has been a continual annoyance. There's currently no clear winner as far as what option is best and it really depends what you value to determine what to choose.

Your options:
1. YUL-YOW-YEG (same flight number, with a stop in YOW)

- Although connecting through YOW might be the fastest/easiest, it's a terrible time-waster given the MLL too far to walk to (given the time constraint) and with YOW being so boring airside.
- If you're an AE mileage hound it's also annoying stopping in YOW and not getting the extra status segment or the extra miles for "connecting". You get fewer miles flying YEG-YOW-YUL (1844) than the other options.
- As you mention the choices of flight times is non-existent.

2. YUL-YYZ-YEG

- Connecting through YYZ not always a treat and I find more likely to have delayed bags.
- MLL always accessible.
- Your best choice for different flight times.
- If you fly J then you're able to fly entire trip in J and get more miles (2170) than through YOW, but it might take a little bit longer to get there.

3. YUL-YYC-YEG

- Not likely to get J service on YEG-YUL
- Fewer flight choices
- Longer travel time than through YOW
- Most mileage from domestic choices (2366)
- YYC MLL has been crazily busy of late and sometimes hard to find space

4. YUL-YYC-Hertz
- Driving YEG-YYC always seems like an ok idea until you have to make the trip, especially in winter. I'd rather sit in the YYC MLL and wait for connection.
- 1866 miles
- Might be more expensive than just connecting????

5. YUL-ORD-YEG
- have never done the trip and not sure of the mileage, but imagine it would take longer and have fewer choices for flight times.
- have to go through US customs