I think YYC's main problem is that WS is short staffed. Creating delays, be it for departure, arrival, baggage claim, etc. Most of the pics you see in that CBC article is mostly that. Not customs related. WS needs to hire back more staff. That will solve most of the problems at YYC.
https://toronto.citynews.ca/2021/08/13/westjet-staffing-shortage/
The issue at YUL is something else entirely and has to do with customs. Not because they are short staffed, but rather because it is taking 5, 10x longer per passenger to process compared to pre-pandemic times. (Checking for vaccination status, quarantine planning requirements, etc). Combine that with the increase of international passengers YYZ and YUL are seeing in the last few months, and the outlook doesn't look too good. When passenger numbers really start to pick up in 6 or 12 months time, customs procedures need to get more streamlined, or else these lineups will get bigger and bigger. it is already a disaster. What will it look like in 2022?