Why do Canadian Airport Codes Begin with Y

I've got some training coming up this week dealing with Canadian travelers and as part of it I was brushing up on Canadian airport codes. There is a serious oddity in them in that they all start with the letter 'Y'. (Well, not all but the exceptions are only trivia. The major ones all do.) I've always wondered why the uniform letter but have never read a good explanation.
My Google-fu was weak and I could find no good reason. The best I can get is that when the codes were being decided by IATA, the Canadian government requested that they all begin with 'Y'. No particular reason for it, they just did. And no, I don't think that's a satisfying answer either. So...I've come up with some of my own.

• As a tribute to Yul Brenner.
  
• Thought that A (eh) was too 'on the nose', you hoser.
• Didn't want to risk a showdown with Cowboy X.
• Use of Q would only encourage Quebecois seperatists.
• Too many 'end of the world' jokes for Z.
• As a tribute to Yellowknife, the only territorial capital in the world named for a colored weapon.
• Enjoy tricky status of sometimes being a vowel, sometimes a consonant.
• Because they are inscrutable Canadians.

Yeah, I have no idea.