John Cena Goes on Date with Mystery Chick, Moving on From Nikki Bella

John Cena is back on the dating scene ... hanging with a mystery hottie in Canada and, apparently, putting his ex-fiancee Nikki Bella firmly in the rearview.

We got this shot of the WWE superstar out on the town with an unknown -- for now -- brunette in Vancouver, and they're clearly having a great time together. Not only were they cozied up, arm-in-arm together ... but the photo agency that spotted them says they enjoyed a 4-hour dinner date!!!

This was their post-meal stroll ... and a pretty romantic one at that.

John's in Vancouver filming a new project, "Playing With Fire." The timing of his new playmate's debut is interesting. We've been seeing Nikki in California hanging with her new bae, dancer Artem Chigvinsev.

We broke the story ... Nikki says she's NEVER getting back with John, and based on this pic ... he seems to be just fine with that.