John Cena made his debut against Kurt Angle. The two had a popular rivalry back in the day.
Source: Kurt Angle
Triple H was John Cena's opponent at WrestleMania 22. Nobody expected John to win but not only he won he became a big deal as he submitted The Game.
Source: WWE
Randy Orton is arguably the biggest rival of John Cena in WWE.
Source: WWE
Edge and John Cena's rivalry will go down in history. The two fought several times in the squared circle.
Source: WWE
The Rock and John Cena had only fought twice but the rivalry was indeed a once in a lifetime kind.
Source: wwe.com
Shawn Michaels and John Cena had a huge rivalry at the time of WrestleMania 23.
Source: WWE
John Cena also engaged in a segment with Roman Reigns. Reigns is the only opponent over whom Cena did not have victory.
Source: WWE
Kane and John Cena gave some of the classics during their time working together.
Source: WWE
Like Randy Orton, CM Punk will also go down as one of the biggest rivals of John Cena.
Source: All Elite Wrestling
Brock Lesnar and John Cena had a fiery rivalry. Cena could challenge Lesnar again upon returning.
Source: wwe.com