It's understandable they would demand it but do you think they are entitled to it?
According to the law, corporate rules, and his employment contract, yes they are entitled to fire him at any time the board of directors want. The CEO almost always serves at the pleasure of the board of directors, they can be let go for any reason, or no reason at all. A common reason is that the board of director just want to take the company in a different direction.
Rousseau was paid C$13.1 million last year, and in return the stockholders demand near perfection. To get the best pay, he must be the best CEO. If he is not the best, they will fire him immediately, and get the best.
The board of directors have a fiduciary responsibility to get rid of Rousseau if he fails the stakeholders. Air Canada was mostly not supported by the Canadian taxpayers, but rather by the Quebec taxpayers. Quebec spent a lot of money to keep Air Canada flying, and they had one demand for that money: Air Canada must speak French. Rousseau spit on those taxpayer, the customers, the employees, and in doing so also the stockholders who will have to pay for his arrogance.
Rousseau arrogantly violated the rules. He was required to speak French, but did not. He had 20+ years to learn French, but did not. He should not be able to keep his job if he cannot meet the basic job qualifications. He was arrogant, and it backfired.
He has reached an obvious retirement age. He was going to retire sooner or later. They had spent the last two years looking for his replacement. Looking at the facts, he chose to retire.
They could have fired him immediately, but that would have thrown damage control into disarray, so they just retired him at the end of the year.
They were offended, hurt, upset or whatever other adjective you want to use, ok so what? They didn't suffer any injury and they lost nothing but he loses his job. That seems unreasonable to me.
Rousseau offended the stakeholders of the company, which if nothing is seen to do about it will cost the company billions of dollars. Air Canada is not a charity meant to pay Rousseau no matter how bad a job he does. If he fails at his job, he will lose his job.
So this "early retirement" is bullshit.
The standard retirement age in Canada is still 65. Rousseau is 68. It can no longer be called "early retirement." By the way, Canadian companies can require anyone to retire after 65 for any reason, or no reason at all.