Yes it is frustrating because of their own faults. How can it be accepted all these years and suddenly YYZ cannot accept it? I can tell you that it has got nothing to do with space on board. It is just making money off passengers. We were a family of 3 and I am a *G. We had 4 checked in bags of which we paid for the first two bags of my family members as then they are entitled to the 2nd bag free. I was the only who had the problem with my carry on. The carry on that never had a problem with AC for the past 4 years and including the previous AC domestic and International flight the previous week.
But I had to pay for my carry on though the 3 of us are entitled to two more free check in bags. The guy on the counter (near the electronic sizer who was charging the passengers for the carry ons) would have none of it. He wanted me to go to a service desk if I do not want to pay to him then and there. And to get it sorted out though I showed him our tickets that says 1st bag has to be paid while the second is free. That meant going to the service desk and then queuing up again on the long queue again. By the way on that day everyone going on AC had to follow the queue even if you know that your bags would fit on the sizer. The security queue had backed up so long too and if I tried that then we would have missed our connection.