I don't think Wade Barrett will win the Royal Rumble. There'll be a point in the Rumble where Barrett emerges, begins to dominate the match-up to the point where he will be the only man actually standing in the ring, and he'll watch the counter tick down as Randy Orton makes his return from injury. The two will then go back and forth and Orton will eliminate him. Orton won't win the Rumble either.
They will then both be involved in the Smackdown Elimination Chamber, one eliminating the other and neither winning the match, leading to a match between the two at Wrestlemania. As for who should win that match? Orton won't need the win as he is close to as over with the fans as Cena is. Barrett beating Orton at Wrestlemania to end the feud would be huge for him and it'd be the final step towards a World Heavyweight Championship match.