In Ontario, as a new parent, you are entitled to take unpaid time off work for up to 37 weeks to take care of your newborn child (i.e., parental leave). This right applies to both parents, and the employer is legally required to provide you with your old job at the end of the leave. The employer is also not permitted to retaliate, or punish you in any way, for taking the time off to spend with your family. Unfortunately employers often consciously violate these rights and returning employees frequently find that either they no longer have a job, or that the job responsibilities or pay have changed.
There is an implied term of the employment contract that when an employee is terminated without cause, they will be provided reasonable notice of termination. (Of course, an employer can avoid the reasonable notice requirement by including an express provision regarding termination in the employment contract.)