Upvote:1
A visa normally does not extend beyond the passport's expiration date.
You can renew your child's passport in Canada. There is a long list of required documents on this page of the Pakistani Embassy in Toronto. I'm not going to reproduce it here. I suspect that you cannot use the online passport renewal application.
Once you have the new passport, you will have to apply for a new visa for your child.
I assume the child has a TRV (Temporary Resident Visa). You can apply to extend/renew/get a new one in Canada. This page discusses extending the stay using a paper form. It's possible to apply online but you may it helpful to read through this page. Highlights include: