As exAC notes, these designators go back to the early years of radio when transmission identifier codes were assigned. And because early airports also used radio transmissions to provide navigation signals, these "stations" had to receive a designator code consistend with normal radio transmitters. As airport convetion, the first letter was dropped. [Yes, Newfoundland had used V as its first letter designator for radio stations until it joined Canada in 1948.] As for why the "Y", since the Americans got into radio a bit earlier than we did with station licensing, all the logical city-related codes got snapped up down there and the precident was started. We had slim pickings for our airport transmitter licensees, so the modified city reference was concieved: VR for Vancouver; TO for Toronto, the original later superceded by YZ about which nobody knows; QR for Regina; WG for Winnipeg... Otherwise we could have aimed for things like VCR or WPG or EDM or CAL that were more descriptive of the actual city name.