Yes, the entirety of C is currently allocated to Canada[1]. The parent comments were talking about IATA codes, though, which aren't allocated by prefix.
[1] https://en.wikipedia.org/wiki/International_Civil_Aviation_O...
[1] https://en.wikipedia.org/wiki/International_Civil_Aviation_O...
https://en.wikipedia.org/wiki/List_of_airports_by_IATA_code:...
But Y is heavily Canadian. We should all just start our own airport. Sounds like a good way to learn about naming. I imagine we will want an airport code staring with YC, so it'll have to be in Canada :P