#3 AJ Styles
While CM Punk and AJ Styles have gone one on one in the past, they never had the opportunity to do so in WWE, as Styles made his debut one year after CM Punk left the company, thus they never had the chance to work against each other in Vince McMahon's company.
Aside from possibly Seth Rollins and Daniel Bryan, AJ Styles is largely considered to be the most skilled in-ring performer in WWE, and during Punk's run in the company, he was widely considered to be the best in the world. So, this match would be an incredible match and an incredible feud both in the ring and on the mic.
In this program, both men could be effective as either a heel or a babyface, although if this is the first feud for Punk upon his return to WWE, the company probably should have "The Phenomenal One" be the heel.