This is historical. At one time each of the councils had their independent graduate scholarship programs. Those were referred to as post-graduate scholarships: doctorate, post-graduate, and master's. In moving to a harmonized approach with our sister agencies, SSHRC and CIHR, we decided to generate a more prestigious scholarship, the Canada graduate scholarship, CGS, at the master's level, and CGS at the doctoral level. They have slightly higher monetary value, but they also aim to recruit a higher calibre of student. That program is proceeding extremely well. They have been devolved to the different universities, the CGS M, for example, and we are proceeding now to look at how we can tweak the system to ensure fairness for the smaller universities with respect to our quota system. But both programs are working extremely well.
On April 12th, 2016. See this statement in context.