Alteration or Deletion of Programming Service
7. A licensee shall not alter or delete a programming service in a licensed area in the course of its distribution except
(a) as required or authorized under a condition of its licence or these Regulations;
(b) for the purpose of complying with subsection 328(1) of the Canada Elections Act;
(c) for the purpose of deleting a programming service to comply with an order of a court prohibiting the distribution of the service to any part of the licensed area;
(d) for the purpose of altering a programming service to insert an emergency alert message in accordance with an agreement entered into with the operator of the service or the network responsible for the service;
(e) for the purpose of preventing the breach of programming or underlying rights of a third party, in accordance with an agreement entered into with the operator of the service or the network responsible for the service; or
(f) for the purpose of deleting a subsidiary signal, unless the signal is, itself, a programming service or is related to the service being distributed.
The DiscoveryHD vs Videotron event of deletion comes, I would suggest, under item (e).