WB is going all out for their upcoming Arrowverse Crisis On Infinite Earths event as Tom Welling and Linda Carter are in talks to return.
A source at Comic-Con has filled me in on details regarding the crossover, which I'll say is bigger than anyone thought.
Tom Welling, of course, is known for Smallville and will reprise his character, with Lynda Carter having played the '70s Wonder Woman. Carter actually appeared in episodes of Supergirl, but she will be back as Wonder Woman.
Update: Tom Welling is confirmed for the crossover.
Update #2: Lynda Carter may be back as Wonder Woman.
Tom Welling and Lynda Carter wanted for Crisis On Infinite Earths
Comic-Con also saw it announced that Brandon Routh will suit up as the Kingdom Come Superman side by side the Tyler Hoechlin Man of Steel.
Burt Ward, the '66 Robin from the Batman series, was also announced at Comic-Con to be appearing in Crisis on Infinite Earths, which is a comic book story that involves multiple Earths and universes, something the Arrowverse has already touched upon but is expanding for the Crisis event series.
More details to come.
Update: DCEU coming to Crisis.
Update #2: Tom Welling confirmed.