#3 Kurt Angle
Way back in 2002, John Cena made his WWE television debut on SmackDown, as he answered Kurt Angle's open challenge, and while the then rookie gave our Olympic hero a run for his money, he was unable to prevail in the end.
It would make sense for Cena, who had his first big match with Angle, to be the one who faces our Olympic hero in his farewell match. On top of that, Angle would likely have no issue with putting Cena over, which would mean that, 17 years later, the former 16 time WWE World Heavyweight Champion was able to get his win back.
Of all the potential opponents for Cena, this is the one that makes the most sense. The two have a long history together, and whether he wins or loses, it'll be easy for Cena to once again leave WWE, as Angle will no longer be around to feud with.