A buddy of mine was called out twice this weekend, once during boarding on his way to YYZ and the other time departing YYZ at transborder security.
His roller bag meets AC's size limits, wheels and handles included. The AC agent wouldn't let him put his bags into the sizer to determine if they were actually within the carry-on limits. The agent at the YYZ trans-border security line was only eye-balling it.
If they're going to implement this properly, they'll need scales and sizers to show the passenger's bag is explicitly oversized/overweight.