A child born outside Canada to parents holding PRC will have to be sponsored for PR by one of the parents.
The tricky part is that as a PR, you can not sponsor from outside Canada. If the couple want to take their baby to Canada to sponsor it, if the baby has a citizenship where it is visa exempt, they should not have a problem. If not, they will have to apply for a TRV for the baby and because the baby is not leaving Canada again, they are often denied. In some cases, people have been denied a TRV but later granted a TRP (ministers permit) for the baby to go with them to Canada to sponsor it. The other alternative is for one of the parents to go to Canada to sponsor the child while the other parent and child stay outside Canada until the sponsorship comes through.