Child born abroad. Has dual citizenship (American and <soon to have> Canadian.
When we fly back to Canada, if the child does not have their Canadian passport yet but they do have their American passport, will they be allowed into Canada?
Yes - will be allowed as a visitor. Apply for a Canadian citizenship certificate and subsequently passport asap if one or both parents is/ are Canadian. This can take sometime though.
They will be allowed to fly into Canada but when you pass immigration, you should explain that the child is a dual citizen and that you have applied for his citizenship certificate.