Can I extend my parental leave?

You have the right to take full leave from work until your child is 18 months old. However, you must notify your employer at least 2 months before the leave that you intend to take it and for how long. So if you have previously announced that you will be on parental leave for a year, and now want to extend your leave, you must notify your employer at least 2 months before the end of that year.
If you have a collective agreement at your workplace, there may be rules that require you to notify your employer earlier or later.