Is there a Canadian law or regulation which requires me to have my Radiotelephone Operator's Restricted Certificate (Aeronautical) on-board the aircraft with me?
This is what I've found so far:
Canada requires you to hold the certificate (Radiocommunications regulations, Part V, Section 33):
A person may operate radio apparatus in the aeronautical service, maritime service or amateur radio service only where the person holds an appropriate radio operator certificate [...]
However, I can't find a regulation saying I need the piece of paper with me.
An example of the wording Canada uses in its regulations to say that you need to actually have the document with you is at CARS 401.03 (1)(d) (regarding pilot licences):
the person can produce the permit, licence or rating, and the certificate, when exercising those privileges.
I can't find that wording or anything like it relating to my radio operator's certificate in the CARS, the Radiocommunications Regulations, the Aeronautics Act, or the Radiocommunications Act.