How long have they've been friends for?

John did a Celebrity gig where the Gillete Young Guns trained Celebs to drive Cup Cars. Carl was John Cena is teacher. http://sportsillustrated.cnn.com/2007/writers/arash_markazi/06/22/cena.edwards/index.html
Also, they did a Young guns commercial together.
http://gilletteyoungguns.com/tv/
It was last year

maybe edwards is trying to hire cena to beat kevin harvick up for him.

They were on NASCAR Live last night. They said they hooked up during the Gillette racing show last year.
It does seem coincidental that he shows up a week after Carl gets his butt kicked.

l am guessing when they probably met at the Gillette Young Gun is commercial.

They were both on Trackside yesterday, according to Cena, they both just seem to click.

Yep,Harvick is truck driver went home sick for the weekend LOL

Actually no, l didn't. l guess that is what l get for not paying too much attention to the pre race show.
But John was in Atlanta for the NASCAR weekend. He was on Trackside on SPEED, & now as l hear on ESPN is coverage & was on Victory Lane as well on SPEED, though he was only shown, not interviewed.

They have been friends since John appeared on the Pop-Culture/NASCAR crossover show Fast Cars & Superstars (by Gillette) that was on ABC for a short time last year. Carl was the one who had to teach John about driving a NASCAR race car.
Since that show, they have also done the latest Gillette Young Guns commercial which features John trying to show the Young Guns how to wrestle but ends up getting beaten up by them instead & Carl is the one who finishes John off by dropkicking him off of the ring apron onto a table.