No law is ever simple but it is a bit simpler in Canada than the USA. Here you don't have to register a work to claim copyright as it is automatic. Copyright belongs to the authour of a work from the moment of its creation and if not ceded to others remains with him/her for the duration of their life. It then becomes property of heirs for 50 years following the authour's death. At that time copyright expires and the work becomes public domain. Copyright of all works by that authour would expire at the same time no matter when each was created or when they were first published or who owns title to the copyright if it was ceded. There are exceptions if the authour is unknown that set the duration to 50 years after publication or 75 years after creation. What the authour has to do is be able to prove that a work is his creation and it can be done by registration with the government but can be done other ways as well.
   That being said international law can complicate things. Hank Snow as an example has only been dead for a few years so copyright will remain for a long time. He was also a duel citizen of Canada and the USA. His early works were created in Canada and his later ones in the USA. The day will no doubt come when a few lawyers will get rich fighting over his copyrights.