I flew air canada on the way to Barcelona and had two separate layover at this airport. One on the way there (a day layover) and one layover on the way back (2 hours)
Flying in for my one day stay layover was easier than the 2 hour layover going through custom. They were not concern at all with why I was staying in Canada for my layover and did not question much. Things were different on the second layover (2 hours) the line moved super slow and the custom officers were 10:1 ratio so they were under staffed. It took an hour to get through that line and they asked a lot of questions. I told the officer I wasn't leaving the airport because I have to make my connection. He questioned me some more. Seriously? ridiculous. It was a little backward because I would be more concerned with people leaving the airport going into Canada. Anyway, they need to have better line controls so people don't miss their connection. I made it to my connection within boarding time. I don't like feeling rushed. It would be nice to have a little time to buy food to eat since I came off a long flight.
Parts of the airport is modern and some were still old. I flew out of D gate and it was modern.