Thanks.
I was hoping Jonathan Joestar would be the John Cena of JoJo's.
Johnathan is a giant mountain of muscle and an excessively good-natured guy, so I could see it from that end. On the other hand, he also values his status as a gentleman and would be appalled by the poop jokes.
Joseph would be ok with the poop jokes, but his entire schtick is making up for his weakness with cleverness.
Jotaro could work. He has a limited move set that features a lot of punching, he has a catchphrase, and he's ok with poop jokes. But he's definitely not the smiley nice guy, he's stoic and a self-aware jerk.
The other Jojos get even further away from appropriate. Josuke's gimmick is that he can heal everyone's damage except his own, the exact opposite of what happens when Cena gets involved in a storyline. Giorno is a tiny fey mafia prince. Jolyne is a badass woman in prison. Johnny is a paraplegic jockey. Even if I expand my search to sidekicks and villains I'm not really coming up with anything.