The plan is currently for Peacemaker to start up its production in early 2021, presumably while the post-production process is in full swing for The Suicide Squad.
It’s not like John Cena isn’t already busy enough himself, with several other projects on the horizon that fall outside the comic book world.
It’ll be the very next thing he works on, which is happening before he starts up on Guardians of the Galaxy 3, though it’s not entirely clear if that Marvel sequel is being pushed back at all, or if Gunn already had that entire time window blocked off for Suicide Squad.