We only saw John Cena wrestle once last year and it made headlines, breaking years-long records for the WWE. For this year, the 16-time World Champion is much more available for the WWE.
As per the Wrestling Observer Newsletter, John Cena's schedule is open to regular appearances in the WWE, at least until April. Specifically, the report points out that Cena has just finished filming Ricky Stanicky last March 4. Because he currently doesn't have big commitments outside of the WWE (Peacemaker Season 2 has likely been delayed), Cena could have a more involved role in the WWE this year.
The past few years saw Cena step away from the WWE as he focused on his Hollywood career. To that end, he's starred in The Suicide Squad, Peacemaker, and F9. He's currently set to reprise his role as Jakob Torreto in Fast X and the franchise's final film.
Theory vs Cena makes a lot of sense, probably more than the initially teased match against Logan Paul. Theory crashed Cena's party last summer when Cena celebrated his 20th anniversary in the WWE.
Since then, the WWE has slowly built up their feud, culminating in the official announcement of their WrestleMania 39 match with the United States championship on the line.
WrestleMania 39 will be Cena's first time to compete at the Grandest Stage of Them All since his Firefly Fun House match against Bray Wyatt at WrestleMania 36.