He's gonna be Barry. Look at the comics and outside media.
Barry has been re-established as the definitive Flash across the board. Obviously, there's the New 52. Then there's the recent animations featuring him as the Scarlet Speedster: Justice League: Doom, Young Justice, Justice League: War, and the upcoming Justice League: Throne of Atlantis. There's the video games as well: DC Universe Online, Injustice Gods Among Us, LEGO Batman, and Infinite Crisis. Lastly, the TV show.
Furthermore, look at Wally's treatment as of late. He was benched for the majority of the New 52's lifetime thus far. Now that he's finally been brought back, he's radically different to the point of being a different character altogether. Not only does he look and act different, but his role is different in the new Flash lore that is being built.
It is highly unlikely that DC will go back on this continuity that they're building. Pre-Flashpoint Wally is a thing of the past and little indication has been made that he'll be coming back. Young Justice is likely the last we'll see of the character as we've known him previously.
That said, I do not agree with DC's decisions regarding the character. I respect his established presence in the Pre-Flashpoint continuity. I also have an appreciation for the vast character development that he's experienced going from a goofy, womanizing teen to the responsible adult and true hero that he became after settling down with a family and launching his hero career head on. I will miss the Wally that we got from late 90's up to 2011 where he disappeared from the comic realm.
That also said, I'm really sick of the Barry hatred that has resulted from it. People have been bashing the character non-stop saying that he was a boring and useless character. They say that he should never have been brought back since he hasn't done anything of worth since the return. They say that he's inferior to Wally in every way. All of those things are absolutely untrue. Even objectively - there's no opinion that can discredit Barry's worth to the DCU overall. Just look at how all of the other characters talk about and remember him while he's dead. Look at what Wally himself says. Regardless of your opinion on his personality, he's far from undeserving of a place within the DCU.
Sorry for the ranting, but I'd just like to point out that Barry is the best choice to start off the DCCU. He is the one that really accelerated (no pun intended) the Flash into popularity in the first place and contributes a lot to lore by way of setting the precedent that the rest of the Flash family of characters followed after him. Though the DCAU tried, there's no way to tell Wally's story without Barry in a way that feels natural without amalgamating or combining the two distinct characters into one. Ezra Miller is most likely going to be Barry Allen.