I am not extremely experienced with flying different airlines (I've flown Air France, Aer Lingus, Easyjet, Air Canada and British Airways - there were some flights when I was young but I'm not sure with who), but with my limited experience Air Canada is by far my least favourite. We just took a return flight to Florida, and if I can I will try to avoid ever flying them again. Unfortunately, I've already got tickets in a couple of months for the UK, so I'm stuck.
Just my opinion, but the cabin crew were the most unfriendly and unhelpful I've ever experienced. The flight was late going down - not a big deal really to me, but in hindsight I realized we didn't even get a 'sorry about that'. Anyway, as I said, my opinion for anyone searching the forum asking the, "what has people's experience been with this airline" question.
They lost my sister a few years ago too - another story!