Who is the other oppenent in wrestlemania with undertaker ?? + When he is gonna return

After the sheild attacks the phenom last friday night maybe he will not appare again until summerslam to play a match but we don't know who is this superstar.
After 21-0 at wrestlemania maybe all of you asked who is the next superstar who will face the undertaker at wrestlemania 30 at 2014 ??
The answer :
1.John cena
or
2.Ryback

But I think it will be John Cena to be an epic show.