Pros
The benefits at Air Canada are amazing. Full dental, 100% paid prescriptions, full pension, and of course travel. I have spent on average 2 months of every year for the last 10 years traveling the world. Usually 3-5 trips a year. Weekends in London, weekends in Barbados, quick runs to Australia or Thailand.... Hard to beat. Advancement is very political, and all airlines are cyclical. So if you can move fast, make the right contacts, don't mind them cutting your salary every couple of years, and don't get laid off, you might find it easy to get ahead.
Cons
I have worked at Air Canada for 11 years and for the last 9 air canada senior management has made it very clear that they feel air canada would be a much better airline if they could just get rid of all their employees. The stress they put us through is often unbelievable and unrelenting. Recognition and feedback is slim. Lower management usually is squeezed pretty hard from above and below, so they really don't have much to do with you if you do your job well. There is no recognition for a good job. I have not had a performance review in 6 years. Unionized jobs are of course based on seniority, so new employees get the worst ride, lowest pay, worst shifts, and first out the door when there is a downturn. There is a lot of bumping around as higher ups cut here and there making it hard to even have a regular schedule. New employees also are often part time working shifts such as 8pm to 2am or 430am to 930am (or both). This, with frequent schedule changes and forced overtime, makes it very hard to have a second job or go to school.