No clue. All we know is that the Legionnaire will be humanoid and male; and even that much is conjecture from the silhouette. Also, the Legionnaire in question is one of the Thirteen, which means that he was extracted from the timeline at some point and for some reason. That's nothing conclusive; but it does suggest the possibility that the Legionnaire may be a brand new character.
On the other hand, nearly all of the other Thirteen have connections to existing heroes (or villains, in the case of Harlequin's Son); so while the Legionnaire may be a brand new character, he's unlikely to be completely original. Perhaps he's someone who could have been (but wasn't) on the roster of the 31st century JSA that got slaughtered in New Golden Age #1? The android Hourman came from the 834th century; perhaps a 31st century precursor to him, who was retroactively involved in the creation of the Legion's time travel technology?
Just wild speculation for now; we literally have almost nothing to go on.