Candle
JCP pretty much nailed what I was going to say, but there are other things he could do.
-Hook him up with Public Enemy. Where better to put a corny white boy rapper than with a bunch of other corny white boy rappers who are over?
-Push him how Heyman initially pushed Shane Douglas. Heyman saw Douglas as the epitome of the high school quarterback. Who better fits that bill than John Cena? Granted, he doesn't have the same gift of gab as The Franchise, but I think he could add his own twist onto the gimmick.
-Push him in a similar way to the Beautiful People in TNA. TNA set out to have a legitimate women's division and tacked on a parody act of what WWE was dishing out at the time with Velvet Sky and Angelina Love acting like Divas. Have Cena come in as the guy gunning for a contract with Vince or Bischoff. He's everything ECW would have hated in a wrestler: in shape, good looks, and five moves of doom. Play off the idea that ECW was being treated like a farm league, so some young rookie upstart decided to take advantage of that reputation and tried to coast his way through without having to participate in the hardcore mentality, and instead wrestled like a WWE wrestler would.
Jim Crockett Promotions Fan
I could see Paul Heyman booking John Cena and awful lot like he booked Tommy Dreamer. The first part of his career he would have been booed and gotten a lot of negative feedback from The Fans until he proved he was as tough as anyone there. It would have been interesting seeing John Cena wrestle Taz, Sabu, Rob Van Dam, Shane Douglas, Eddie Guerrero, Chris Benoit, Eddie Guerrero, Dean Malenko and a whole host of others. Can you imagine The Sandman beating John Cena with a Singapore Cane? Can you imagine The Dudley Boys Power Bombing John Cena threw a Flaming Table?
Geese
I could see him challenging Rob Van Dam for the TV title. It would be see-saw matches with Cena pushing RVD to the brink but coming up short in the end. Cena could be in triple threat matches for the ECW Championship pitting Mike Awesome vs. Mastao Tanaka. I could see him being a titleholder, eventually, but I wouldn't push him to the moon right away.