From my days in the radio biz, I found that many stations used the Cancon regs as a maximum amount of Canadian music to play as well as a minimum.
For example, if the station had space for 8 current Canadian hit tunes in their rotation and, one week, there were 10 great new Canadian songs, the station wouldn't make room for all 10. They'd stick with the 8. At the time I was at CITI-FM here in Winnipeg, the regs stated we were to play 20% Cdn music. If the percentage ever hit 22%, we got hell from the management. Deplorable, if you ask me.