You cant trade in PC games
Post how much you think you'd get trading in your mw3, or what you have already gotten for it
Mess With Success
^ At least ones in steam. So yeah. Unless you sell the account you activated it on, you are stuck with it. Xbox however, it depends on who you ask. Someone who wants the game would pay more than someone whos just looking to toy around with it.
But honestly, dont expect much, unless you are selling it for the xbox.