Given recent form Vika is the favourite in this match. Anna could do herself a lot of favours ranking-wise by winning this one match. It will be very tough.
I concur, Azarenka is a slight favorite. Though I think that Azarenka has the kind of power game that clay really hinders. Whereas Anna's game is more balanced and thus less likely to be hindered by clay (or aided by glass).
Yes, one would think that clay doesn't particularly suit Azarenka's game, but she has a pretty good career record on this surface, with wins over the likes of Schiavone, Dulko, and Cibulkova, among others. Anna leads the H2H 2-0, but I don't think that means a whole lot right now.
A win on clay over an in-form Azarenka would be noteworthy. Not sure what to expect from this match, except probably lots of breaks of serve.