nono, the baby is born is Canada, hence Canadian citizen already, and does not need to be added for the PR application....
congraaaaaaaats Basil that's great news it must be a wonderful feeling
i think yeah u need to tell them - it's also proof for the genuine relationship and maybe they will speed up the process to b with ur son asap....i think u also need to send them one updated form, supplementary family form or smthg like that, where u list ur mom, dad, siblings and children....now u'll have to list ur son too, u can also include a copy of the birth certificate....that's what i would do
as for how, i'm not that sure: maybe email to them or in case specific inquiry portal, u can also upload the documents there and u'll get confirmation...see how islamabad members do it successfully
good luck!!