Yesterday I flew KLM from Pearson to Amsterdam from T3. It was easy, we had perhaps 30 people in front of us to check in and we absolutely sailed through security, no more than 5 mins. Our checked luggage arrived with us, no issues. In advance of our trip i asked a friend who‘s a VP at Pearson if I should be worried and he said no, as long as you’re not flying to the US or anywhere via Air Canada we’d be fine, since the issues are lack of US customs and Air Canada check in staff and luggage handlers, plus Air Canada booking flights they know they didn’t have sufficient qualified pilots to fly. My friend said if you’re flying from T3, which uses a different baggage handling firm and avoiding the massively backlogged US preclearance, you’re fine. And we were.
If you’re flying T3, and not to the US, my experience is you’re fine.