All the DLC you've purchased and the assorted objects you collected in LittleBigPlanet and its sequel will be usable in LittleBigPlanet 3.
LittleBigPlanet community coordinator Steven Isbell wrote in the PlayStation blog, "Every single Costume Piece, Material, Object, Music Track and any other creative goodies that you have collected in your previous adventures with Sackboy will be able to be imported into LittleBigPlanet 3!" and getting all of your old previously purchased DLC with re-buying it will just be a matter of visiting the in-game store. You will also be able to access and play all of your previously published levels, as well – a detail that was revealed during the game's announcement.
Isbell promises that at the time of launch, a convenient FAQ will be available detailing how players can access all of their old content in the new game.
LittleBigPlanet 3 is coming to PlayStation 3 and 4 on November 18.
[Source: PlayStation Blog]