Most wrestlers juice in some way or form, just to be bigger and catch Vince's eye. Once they are established, no one really cares what they look like...Let's look at HHH, Angle and Booker T. Both were very big back when they started, made a name for themselves and cut down/came off the sauce.
Funniest thing I ever heard was both Jake the Snake and Roddy Piper admitting in an interview that they used the sauce
As for Cena, very hard to tell. I would hate to be his brother tho, John making a million plus a year doing what he loves and Matt doing whatever, prob not making 1/10th his brothers earnings...