I recently wrote to CATSA to find the status of the Nexus/Global Entry lines. Here's their response (dated Nov 2):

... At the start of the pandemic, CATSA closed all Trusted Traveler (TT) lines due to the significantly lower volumes of traffic. We are monitoring upticks in traffic, and will gradually reintroduce TT lines as traffic and demand increase and resources allow. For now, we are pleased to share that a few are currently open at our busiest airports, and all airports with TT lines have reintroduced Queue Jump services to allow NEXUS cardholders to bypass the main queue and be directed to the next available line. ...

Can anyone confirm if "the busiest airports" (I have to assume that means YYZ, YVR,YUL, and YYC) have re-opened their Nexus lines?