About the GNU Public License (GPL) version x.
It's clearly mentioned in GPLv2 and GPLv3 declarations that you must apply this version or, at your option, newer of the license.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Source - How to use GNU licenses for your own software
So; the parts of your program using only GPLv2 submitted code could be redistributed under GPLv2 or under GPLv3, if you want.
The parts using only GPLv3 under GPLv3.
And so, your program should be redistributed under GPLv3, since GPLv3 contains everything GPLv2 contains plus added content.
And since there is 3 licenses; I think you should apply the GPLv3 on your program, plus the other license, and, as long as the licenses do not interfere with each other; you probably should apply both (GPLv3 and CC).
If the license interfere with each other; you better should contact CC's admins, the GNU's admins (or the Free Software Foundation?) and Open Game Hearth admins.
I'd recommend to put all the sources and headers under GPLv3, the documentations as well.
And all the arts (drawings and such) under the CC license.