What is notice?
An abundance of misconceptions exist notwithstanding the relative simplicity of the answer. Notice is... just that. Notice. It could also be called forewarning.
If an employer tells an employee that their employment will end at some future fixed date, notice has been given.
Whether that notice is sufficient or (in the language of the case law) "reasonable" will depend on a number of factors such as the dismissed employee's job, length of service and age but many additional factors might factor into the equation too.
One should be careful not to confuse reasonable notice with the amount of notice required in employment standards legislation. Legislated amounts are MINIMUM amounts only. Almost every worker in Canada is entitled to more than those minimums.
Being terminated without notice or on insufficient notice is one of the elements of a wrongful dismissal.