When John Cena makes his return to WWE TV on the July 4th episode of SmackDown, emanating from Phoenix, Arizona, he will do so as a "Free Agent" as seen at the end of this promo vignette that ran last night on Raw.
This would seem to back up a report that came out yesterday from PWInsider, which states that Cena's Free Agent status would allow him to appear on both SmackDown and Raw, and also to feud with superstars from either the blue or the red brand.
Cena has been gone from WWE since WrestleMania 33, when he and girlfriend Nikki Bella defeated The Miz and Maryse in a mixed-tag match, after which Cena proposed to Nikki. After Nikki said yes, they both exited WWE, she to rest her neck and heal from some nagging injuries, and he to film two movies, "The Pact" and "Daddy's Home 2."