Lesnar winning the WWE Championship from Orton on Raw would just be terrible. If they're gonna give Lesnar the strap (they're not, at least not yet), then make him look like a beast by putting him in the chamber match (in his home town no less) and having him win it there.
Pretty obvious that it'll be Dean Ambrose losing the United States Championship. I think most everyone has figured that him losing the US Title and blaming Rollins and Reigns for not being there for him during the match (and perhaps the two of them telling him in return that if he's "the boss" like he says he is, he shouldn't need their help to retain the championship... especially with Reigns calling him out lately on how long it's been since he's even defended the belt like a true champion should) is gonna be used to cause further tension between he and the other two. This is especially the case considering they'll be coming off a huge loss just one night before to the Wyatts at Elimination Chamber, and Ambrose will likely be playing the blame game anyway. This will then eventually lead to the inevitable breakup of the group within the next couple of weeks or so.