Yeah, Langston seems like the logical choice. He said recently that a match with Batista was his personal dream match for Wrestlemania, plus the 'E puts a lot of stock into Langston as one of the future stars of the company, so it makes sense to have Batista put him over. Big E would have to drop the IC Title before then, though.
A match with HHH is something I wouldn't consider off the table either, though. They have history (being former partners in Evolution, and the fact that Batista won his world championship gold by defeating HHH at Mania 21 in 2005) and I could see McMahon announcing on-screen that the man he's chosen to defend him at Mania is none other than a man who HHH should fear stepping back into the ring with... "The Animal" Batista! Keeping in mind that Batista has said on record that if he ever made a return even for just a short stint, HHH is one of the names he'd like to work with again. (Here's hoping for the opposite though, as Punk or Bryan getting the match with HHH is much more beneficial and makes more sense to me.)