I hope this isn't the case at YYZ, I routinely arrive an hour before flight (NEXUS/GE)
However, 2 data points: the tuesday AM after president's day was an absolute sh-show, NEXUS took a half hour (security+CBP), with lineups to the security, and then a long line into the nexus machines, and a long line to the CBP officer. He did ask the purpose and if I'd been to china, but that's it. (It usually takes no more than 10 mins, maybe +5 on a busy day)
Last saturday was going thru with family and arrived 1;15 out; and security was halted due to cbp. Waited about 15 minutes before they restarted, and when they did it went quicker than the prior time, no lineup for kiosks and short one for an officer.
Both were AC flights though. Regardless of whether UA is really doing this, I would certainly advise if going thru YYZ to add some time to your normal routine, a LOT more if you're non-NEXUS/GE.