CGP Grey recently released a video on the history of airport acronyms, e.g., LAX. He briefly said that you may wonder why codes for Canada started with Y and formerly CY, and that it traced its history to the telegram “but that’s a story for another time”. I don’t feel like waiting.
Why did the International Telecommunications Union denote CY for Canada?
Why: Result of negotiations. 1947 at the International Telegraphic Convention, the post-World War II radio community rearranged itself. There was large demand for new ITU prefixes, and Canada, which had a block CF-CK, wanted more prefixes.
It got some – but since other states had been assigned prefixes starting with C as well (e.g., Cuba, Morocco, Portugal), there was no chance to "continue" the existing block. So a new block, CY-CZ, was created for Canada.
And that's how Canada got CY. Feels pretty anticlimatic, doesn't it?
that it traced its history to the telegram
I guess he's alluding to the non-obvious fact that aeronautical prefixes were commonly derived (but not always so) from the ITU prefixes, and that the T in ITU stands for "telegraphic".