This form must be completed for a minor under the age of 17 if a minor is going to Canada to study but is not accompanied by the parent(s) or legal guardian. A Custodianship Declaration states that a minor must be looked after by a responsible adult in Canada, who is simply referred to as a custodian.
The minor/child will need a letter of consent from his/her non-accompanying parent(s) or legal guardian and a duly completed Custodianship Declaration – Custodian for Minors Studying in Canada (IMM5646E) form, from their Canadian custodian.
You can download IMM5646E form here