It's been confirmed as not being The Warden, which makes sense because the Warden was never voiced. Voicing The Warden - while a catchy name for a non-existent PR video - would risk breaking the experience for players.
To me, it looks kinda like Sebastian, but unless you kill Anders he checks the hell out, and he's not a Grey Warden or even a tangentially important character at this point, despite Starkhaven's relatively significant status within Thedas.
Also, for those wondering why Anders hasn't been announced as a part of DAI, and why the potentially trolling VA for him is saying he hasn't gotten a call for DAI, Sebastian's potential final vow to a Hawke who leaves Anders alive is to raise the army of the largest city-state on the continent and kill him. So there's a good chance Anders is dead as a doornail or "mysteriously missing" no matter what, and that would certainly be the easiest way to handle that situation.
And who knows what trouble Hawke got into after Kirkwall? Since Hawke's father was a part of the Wardens it's not unreasonable to assume that in the face of the rifts they would form some kind of connection. I'm leaning on new character, Wardens have notoriously short lifespans so it's unlikely to be anyone we know - especially if we don't recognize them. King Alistair would probably never be caught dead in standard Warden plate, and drunkard Alistair probably wouldn't be showing up to fight something as bad as the darkspawn again. And dead Alistair is dead.
I wouldn't be surprised if that slot got filled by a returning character, but I doubt this specific one is anyone we've seen in the games before.