The next Call of Duty game will allow players to bring forward content from one game to the next. For example, any content you’ve bought or unlocked in Modern Warfare 2 will be available in Modern Warfare 3.
All weapons, store bundles, skins, operators, and anything else you might have acquired fall under this category. However, if the content you’re proposing does not have a basis in Modern Warfare 3, it will not be available. For instance, if you have a skin for a melee weapon that does not exist in Modern Warfare 3, you will not be able to use it.
It’s clear that Modern Warfare 3 will not allow you to unlock anything you already own, but you can use everything you own in the game. Modern Warfare 3 has a comprehensive FAQ that examines every possible scenario and confirms whether or not the item will continue.