IMDb has been updated which lists Grant Gustin as The Flash for Injustice 2, and while IMDb is not the best of sources, Stephen Amell did provide voice work for the Arrow DLC in the first game. In addition, it seems Katie Cassidy may be providing the voice and basis for Black Canary in Injustice 2.
As it's basically just speculation at this point, it's unclear if Grant Gustin will be providing the voice of The Flash for an Injustice 2 DLC based on the TV series or for the entire game.
Fellow CW TV actor, Neal McDonough, who played the recent villain on Arrow, provided the voice of The Flash for the first Injustice: Gods Among Us video game.
In development by award-winning NetherRealm Studios, "Injustice 2" features a massive roster of DC Super Heroes and Super-Villains and allows players to build and power up the ultimate version of their favorite DC characters. The game will be available for PlayStation 4 and Xbox One in 2017.