When will the Canadian ADS-B satellite system be implemented?
This Advisory Circular, although from 2011, is still current and indicates that there will no Transport Canada ADSB mandate (being regulatory, it's not up to Nav Canada).  It appears the policy is to foster voluntary adoption of ADSB over time, and Nav Canada will create an environment where aircraft operators will get operational benefits by adopting it.  

So the commercial world will likely switch over fairly quickly, while GA operators and private owners will do it gradually as the costs of the systems come down, and anyone who doesn't want to doesn't have to, and can continue using Mode C. I imagine that later on, when the system is mature, say in 5+ years from now, and GA ADSB systems are dirt cheap, TC/Nav Can will likely decide it's time to phase out surveillance radar completely, and then it'll be mandated for anyone that wants to operate in transponder airspace.