To be clear, the version of Future Trunks confirmed is the one from Dragon Ball Z, not Dragon Ball Super.
Dragon Ball FighterZ is a 3-vs-3 team battle fighting game in development by Arc System Works, the same developer as the acclaimed Guilty Gear fighting game franchise.
Responding to a question on Twitter, Joey Cuellar, who is the director of Chief Executive Officer of EVO, the version of Dragon Ball FighterZ at the event will be a build that includes Future Trunks.
It’s possible the Dragon Ball Super version of Future Trunks and other characters unannounced at this time may be playable as well, but as of right now, the roster of characters is Goku, Vegeta, Teen Gohan, Frieza, Cell, Majin Buu, and the DBZ version of Future Trunks.