Only a suggestion ......
A Montreal radio set up to scan:
You would have controller reception on all 3 frequencies. 133.225 is the high sector (FL290 and above) to the east, from Montreal to the Moncton/Boston FIR boundary's, and is linked via relay with 123.925. 134.400 is the high altitude (FL290 and above) to the west from Montreal to the Toronto FIR boundary, and is linked via relay with 127.875. This would give you coverage of all the Montreal high sectors in their southern area. 132.350 is the low sector to the east and covers YUL arrivals from the east via the OMBRE/MAIRE stars, and YUL departures eastbound. These sectors can get quite busy with NAT traffic at times, so any more frequencies would be too much. So ONLY those 3 would be best.
You can hear YUL arrivals from the south via PLB.NAPEE on the ABCOT star, and southbound departures via ALB, on Boston 135.700, good coverage of this sector can be found on the KBTV Burlington Radio.
To the west a radio in Ottawa would be ideal scanning Montreal on 134.975 and 128.775. Both antenna transmitters are located in Ottawa, so controller reception would be good. 134.975 covers arrivals into YUL via SYR/ART.MSS on the FRANX/CEDAR stars and YOW arrivals via ART and MSS on the CYRIL star, as well as YOW departures via ART/MSS and V300-YJN. 128.775 covers YUL departures westbound towards YOW as well as YOW arrivals via YUL, this frequency is also linked via relay with 126.575 which covers YUL arrivals from the north and west via YMX, as well as YUL departures westbound via YYB and YOW departures northbound. Both FL280 and below. DJ