Yes, you need more proof the marriage is genuine and was not entered into just for immigration purposes. The IAD means by 'more proof' different proof than you originally submitted. That is, more of the same types of proof you originally used will not be enough. (Though certainly include more proof of contact, visits, etc.) The baby is certainly new proof - usually a child is enough on appeal to win, though because you were denied the second time after the baby was born, it may not be enough here. The visa officer did know about the baby, right?
The proof you need is that the marriage is genuine now, and that it was genuine when you got married. I have seen an appeal that was denied because the IAD 'judge' believed that the marriage was genuine at the time of appeal, but still thought that originally it had not been genuine. It is hard to prove the intentions of the foreigner at the time of marriage. Some proof that has worked has been: 1. showing just that the marriage has continued and developed since the first refusal - if the foreigner really did marry you just to get into Canada, he would probably give up after losing the appeal; 2. the birth of a child - this is not conclusive, but usually people will not have a baby just to pretend their marriage is real; 3. going to live with your husband in his country or some other country is really good proof, but of course can be difficult to arrange.