Your only viable and logical options to face Taker at Mania are Triple H, Cena and Orton.
Retribution for retiring his best friend, a massive heel turn.... either option would work well. Trips is one of the few believable options for a victory over Taker at Mania.
Cena is one of the last "dream" pairings for Taker at Mania. If anyone could legit go over Taker at Mania, it would be Cena. Also insert the possibility of Cena's heel turn in order to attain said victory.
Orton has had a stronger year than anyone in the company and has just about surpassed Cena as WWE's new superman and new found Austin'eque anti-hero. The most over guy in the company would surely be an interesting option for Taker at Mania.
Anyone else is just asinine. Sure you could throw a young talent at Taker...IE.. Drew, Sheamus, Miz, Teddy... though anyone who would perceive any of these guys as a legit threat to Taker's streak is smokin some serious shit.