Celene has noble and progressive ideals that can quite possibly lead to true equality for the elven people in Orlais, but the evidence shows that she easily cracks under pressure and is willing to quickly abandon said ideals the moment they endanger her role as Empress. I suppose she rationalizes that and many other unsavory acts she's committed by telling herself that if she loses power then no one in Orlais will support the elves. Still, you can't murder three thousand elven citizens and seriously hope that they'll still see as their human savior. Sure didn't work on Briala.
So Celene gets no support.
And Gaspard? The man's a chevalier, you know those guys who are feared by their own people because they have almost no accountability. Those guys whose "honor" allows them to get drunk and go off and murder any elf that's unlucky enough to be near them at the time. The man's just as manipulative as Celene, if not more so, and he openly plans to restate a war with Felelden in the hopes that it will "unite the nation." What the heck does that mean? You're saying that a war that will cost the lives of tens of thousands will bring your empire together? How about you just be a good emperor and use your political know-how to unite the flipping empire. Oh, and his sense of honor. Honor is bovine manure. Just because the man doesn't torture people doesn't mean he's a saint or even trustworthy, it just means that out of all the underhand and vile things he can do, torture won't be one of them.
So Gaspard gets no support.
Which leaves... Briala. Freedom fighter who wants to give the downtrodden a chance of actually equality and perhaps a homeland of their own. Yeah, she's the only see candidate that I see who has her priorities and values straight. Total support given. At least for the moment anyway. Really can't make an intelligent choice until DA: I comes out.