I have reviewed the competition statistics for the last few years.
http://www.nserc-crsng.gc.ca/_doc/Students-Etudiants/2017StatsScholarships_e.pdf
(change the year from 2017 to other years)
On page 3 and 4 of this document you will find the success rate of each committee (usually the same across committee, minor differences).
The overall success rate for CGS/PGS combined is about top 42~47% for the last 4 years. Success rate for CGS is about top 20%.
I am ranked in the middle of the PGSD pool (halfway between 20 and 45%) so I really need everyone who got CGS in my committee to decline so I can move up to the CGS Any CGS winner at foreign institutes wanna trade?