#2 Bray Wyatt
This seems like both the most likely and logical option considering the connection between Orton and Wyatt. They've been locked in a storyline together for months now, ever since The Viper decided to join Wyatt's clan, with many people fearing that it would be a short-lived storyline.
However, it's gone on for quite a while now and Mania feels like the perfect place for a blow-off match.
The Eater of Worlds could win the title inside the Chamber before defending it against Orton, with Randy turning his back on Bray at the soonest possible convenience in order to begin the feud. It would shoot Wyatt straight up into the upper echelons of the main event scene, and it could finally lead to Wyatt's first victory on the grandest stage of them all.
We move onto a man who these two know quite well.