Don't have very good idea who the favourite was before these old tournaments but think that in 2005 the two biggest favourites were Anand and Leko.
Topalov had a great 2005, he for example shared first with Kasparov in Linares after beating him (while Leko drew all his games), won also Sofia clearly after beating both Anand and Kramnik, and shared second in Dortmund (ahead of Kramnik and Leko, after beating the latter). But Leko had also done fairly well, winning Wijk in the beginning of the year.
The betting site Betsson ranked Anand and Topalov as the top two, but Leko wasn't far behind:
http://en.chessbase.com/post/short-challenges-kasparov-who-will-win-
With hindsight it's easy to imagine Topalov as being ranked further ahead of Leko than he was, since he soon would be #1, while Leko never reached top 3 and was already fading, but that was difficult to know at the time.
One unusual thing with this tournament was that it was the maybe first round robin World Championship/Candidates where the favourite or second favourite didn't win. Botvinnik won in 1948, Bronstein in 1950, Smyslov in 1953 and 1956, Tal in 1959, Petrosian in 1962, Topalov in 2005, Anand in 2007, Carlsen in 2013 and now Anand in 2014.
Don't have very good idea who the favourite was before these old tournaments but think that in 2005 the two biggest favourites were Anand and Leko. Topalov also had shown promissing form but still it was a big suprise to see how he totelly destroyed the field in the first half. The greatest performance of his career thus far.
Anand this year was definitely a big suprise. Opinion of the general public is one thing but what's notable that even the experts seemed to write his chances off. I also didn't think he still had it in him but glad to be proven wrong.
It should be pointed out that Smyslov & Keres were considered as favorites in 1959, instead of Tal. Many predictors were sceptical on Tal`s ability to win such a strong and equal tournament.
Also Bronstein in 1950, Smyslov in 1953 & 1956, Petrosian in 1962 and Anand in 2007 were considered as one amongst the 2-3 favorites.