The law and details varies by province/territory in Canada, but in every single one of them you are due form of notice/pay in lieu of notice. I.e. they have to pay you for X weeks after they tell you they are firing you, they might require you keep working for those X weeks.
I really like the Alberta model[1]. Employers are required to give a few weeks notice when firing without cause, and employees are required to give a few weeks notice when quitting without cause.
The notice periods are not excessively long, but they give both parties a chance to prepare for the change. A few weeks might not be enough time to hire a new employee or find a new job, but it should be enough to put together a plan.
The ability to fire or quit without cause seems like the part of 'at will' employment that's most important to economic efficiency, so it's nice to have a kinder system which still includes that.
