It existed before 1979 - 1978 was when David Marsden took the helm, and it became the station that it was famous for.
It actually went on the air in 1960, simulcasting CHIC-AM - it was known as CHIC-FM. In the 1970's it started broadcasting rock during the day, simulcasting CHIC-AM still at night. With a transmitter power of 857 watts ERP mono, just enough to just cover the town of Brampton, it didn't have a lot of audience. Up to around 1975, the CHIC AM control room operator spun LPs from the third turntable in AM master control. Nonstop full play of each side of the LP was the norm - with just a break by the AM operator for ID and to flip the LP over. The music was picked by the AM operator prior to their shift. Some of those on air people were Dave Gordon, Mike Lynch, Steve Martek, Rich Elwood, Ted Woloshyn, Scott Cameron. Any type of music was picked from the library randomly. Usually heavy metal.
This was the beginning of CFNY. Listeners loved it and at times requested more of the same, which was obliged. Sometimes missed by the operator, the LP would finish and listeners would call in to complain of the dead air. In 1976, a new FM studio was built just up the road from the old studio in Brampton on a very limited budget. Engineers Mike Hargrave Pawson and Steve Martak built the new studio and a new transmitter site in Georgetown to increase the coverage from 857 watts to 100 kW ERP.
In July 1977, CHIC-FM officially became CFNY-FM. The phrases "Canada's First New Youth" and "Canada F---s New York" have been cited as backronyms for the call sign. Anyone working there at the time was fired, and a whole new team was brought in. David Pritchard, CFNY's first program director, previously a late night DJ at CHUM-FM, gave the station a little more structure and hosted specialty programs of reggae and blues music, and a nationally syndicated (and popular) Beatles show. Unfortunately, conflicts between Pritchard and the Allens led them to fire him for refusing to, as he put it, turn the station into a conduit for "shallow hit-oriented Pablum". David Marsden, who had started as an announcer, became program director of CFNY in 1978.