Our firm deals with employment law. Feel free to PM me if you have any more specific questions.
Generally,
Duhaime has a wealth of information available for you to digest. An employer can fire an employee for no reason at all provided they give that employee reasonable notice of the termination. The period of reasonable notice is determined by considering a number of factors including the length of employment, the age of the employee, the type of job, etc. Provincial employment standards legislation sets a minimum period for notice but common law will serve to extend that period. Rather than allow the employee to work during that period of notice, they can offer the employee pay in lieu of notice. Why keep an unmotivated employee around, right?
They say the rationale behind working notice is to give the employee sufficient time to make alternate arrangements and get a different job. I imagine it would be an awkward situation to be in: expected to come in every day as per before and do your job knowing that in two weeks (or whatever) your job is gone.