My child and I are both Canadian, but my husband is not Canadian.?
As Joan Lockwood suggests, getting a replacement passport by making contact with the nearest Canadian embassy, High Commission or whatever would be the place to start. After all, passports are lost/stolen/expire all the time. If you have kept a copy of the passport, or at least the details of the passport number, date and place of issue etc it will probably help. If your husband is your childs father there may be issues about taking the child to a different country. This can open up a whole range of issues and problems.