Brandon Routh is set to return to the role of Superman in this year's Arrowverse crossover, but that means there'll be two actors playing the Man of Steel - so how will that work? Prior to the Arrowverse's big presence at San Diego Comic-Con 2019, word broke of Routh's part in the upcoming Crisis on Infinite Earths crossover event, which sees him reprising the role he first played in 2006's Superman Returns, but the Arrowverse already has a Superman in the form of Tyler Hoechlin.
Although the initial report on Routh's return suggested that he and Hoechlin would be playing the same character in different time periods, the Arrowverse does already have a much simpler way of introducing Routh's Superman and allowing him to interact with Hoechlin's Big Blue Boy Scout too: the multiverse
This is something the Arrowverse has already played around with a lot: John Wesley Shipp played Henry Allen on Earth-1, Jay Garrick on Earth-3, and finally was introduced in the Elseworlds crossover as the Barry Allen of Earth-90, establishing that there are multiple Barrys out there with different actors playing them. There have also been hints that John Diggle is the Green Lantern in another universe, which again allows for multiple versions of characters, and actors to play different parts, hence how Routh can be both Superman and Ray Palmer/The Atom from Legends of Tomorrow.
The current Arrowverse Superman, which is the one played by Hoechlin, was first introduced in Supergirl's second season (having been teased in its debut run) and exists on Earth-38 alongside his cousin Kara Zor-El. With so many other Earths already existing in the Arrowverse, then there's the potential for Routh's Superman to be a version of the Man of Steel from just about anywhere else in the multiverse.
This makes even more sense considering that the crossover is Crisis on Infinite Earths, a long-teased event in the Arrowverse, which in the pages of DC Comics finds the Anti-Monitor attempting to destroy every Earth that isn't his own. This was already set up by Elseworlds, but now the Arrowverse can truly build on it across Arrow, The Flash, Supergirl, and Legends of Tomorrow, and it means the door to the multiverse is open even wider than it's ever been before. The Arrowverse crossovers always like to have great fun with the possibilities opened up by alternate universes - such as the heroes fighting evil versions of themselves in the Crisis on Earth-X storyline - so introducing multiple versions of Superman fits right in with that ethos.
Superman plays an important role in the Crisis on Infinite Earths storyline, although it's likely the Arrowverse will be looking to mix things up quite a bit. It's already set up for Green Arrow to die in the event, as opposed to The Flash, and if Routh's Superman ends up taking the death of Supergirl from the comics, then it would mean it can have a big crossover moment while allowing the Arrowverse to have one Superman left in the form of Hoechlin's Clark Kent.