This happened to a friend of mine who tried to land but left their newborn at home.1. I am assuming you are the principal applicant so you would definitely need to land before or at the same time as your dependents. However, your unborn child was never included as a dependent. Therefore, once born and you have his/her birth certificate, passport, etc. , you need to inform IRCC. Even if it is a newborn, they still need to be vetted by IRCC. You cannot just put them on a plane and have them enter Canada just because you and your wife have PR. Your child does not.
2. You could land after your child is born. It depends on what is the cut-off date to make your first landing (generally, one year from your medical exams). You won't know what that date is for certain until you receive your COPR.
3. That would be up to IRCC to decide. Naturally, I believe that is something they should allow since you cannot leave a newborn behind but it will be up to them to decide.
Also, an important note that your Proof of Funds will need to be updated to show that you have sufficient funds to cover the additional family member.
Disclaimer: The information above is based on my knowledge and understanding of IRCC procedures and policies. I would recommend reaching out to a competent immigration lawyer who would be able to better guide you.
He was advised at the border to go back home and reapply to include their newborn. He was told he could land but that he should be ready to forget about the newborn as it will be very difficult to convince anyone that was his child.
Long story short, He went back and included his son in the new application and it took another six months before the application was approved!