I wouldn't say there's no way Bryan will lose to Triple H at Mania. I think Triple H beating Bryan is a very possible thing. Not saying he's going to bury him or anything like that, but I can see some sort of staged finished for that scenario, more than I see Bryan going over Triple H cleanly.
I think there'd be more possibility of Bryan losing if it was on a B-PPV, like Punk/HHH at Night Of Champions 2011. But I can't see that happening. There are similarities between the Summer Of Punk two years ago and the push Bryan is receiving currently, but things they did wrong with Punk two years ago, they're doing right with Bryan now. Bryan not only went over Cena clean as a whistle, but HHH turned heel (something we thought would happen with Punk but it didn't) and Bryan is now in a feud with HHH and the Corporate structure that is currently firing on all cylinders. With Punk, they dropped the whole Punk vs WWE after NOC and he even began making jokes with HHH, just 1-2 months after insulting him and the entire McMahon family. He even tag teamed with the man. And they put HHH over Punk in the midst of all of it, so the correction there that I'm aiming for is that they won't make the same mistake with Bryan.
Wrestlemania is typically the place where baby faces get their biggest shining moment and they are taking great care it seems with pushing Bryan. Like I said, HHH does have a good track record of putting people over at Mania, despite speculation on who he's held down elsewhere - Benoit, Batista, Cena, Orton somewhat. It's been documented that he is fully behind Bryan in real life and so I'm willing to give him the benefit of the doubt that he's been willing to put over Bryan at Mania. Let's not forget the Bryan/HHH match could involve the power struggle between Vince and HHH with Bryan fighting for Vince's side of things, which makes a Bryan victory that much more plausible.