Upvote:5
The photocopy only applies if you are still married. If you're divorced, the most important thing to have is the custody document. The authorization letter is optional but is very good to have. Ultimately though, these are just recommendations, they aren't specified in the Immigration and Refugee Protection Regulations. The immigration officer is responsible to use his/her discretion in determining whether you have the legal right to accompany a minor child. If you believe there would be any reason for an immigration officer to deny your request to enter based on a custody issue, it's advisable to consult a lawyer ahead of time.
You may be able to get a sense of what they want to see in the authorization letter here: Consent letter