Actually, my thumb worn copy of Canadian IFR (instrument flight rules) ground school course text written by Micheal Culhane, says:
"Although the naming of Canadian airports and weather stations can seem confusing, here is a brief explanation. Originally, in the 1930's, Canada used two letters for identification of a weather reporting station. Additionally, preceding the 2-letter code, was placed a Y (meaning "yes") where the reporting station was co-located with an airport, a W (meaning "without") where the reporting station was not co-located with an airport, and a U where the reporting station was co-located with an NDB. An X was used if hte last two letters of the code had already been taken by another Canadian ident, and a Z was used if the locator could be confused with a U.S. three letter ident. ... The ICAO names are in a 4 letter format starting with a C for Canadian airports." (section 2.18 pg 64)"
For those of a pedantic bent...