I think Bennati is fairly certain not to ride the tour, although he'd certainly be a good help. He will go for stage wins at Giro and Vuelta as far as I know, and he said he was unlikely to ride all three GT's.
Monfort is, according to Andy, 95% sure to ride the Tour. It makes sense - he can climb pretty well but will also be a great help in the TTT and when it comes to pulling on the flat. I could see him taking over from Cancellara at the bottom of a climb.
Another possible candidate is Joost Posthuma. His season has not been great so far, but if he is in good shape he might be a serious competition for O'Grady, and mainly for Voigt. Everyone wants Voigt to be there (well, maybe not anymore since the radio debate), but if he's not the strongest, they might have to leave him at home. Also Posthuma will have raced almost the same program as Cancellara - if the two click, Cancellara might request him being in the TdF line-up as well.
Feillu will also have to prove himself, which he'll be able to do at the Giro. It's only his third season as a pro, and he only rode one GT so far, where he didn't do domestique work - Oliver Zaugg with his 7 GT's (granted, he never rode the Tour de France) might be a safer bet. He also proved himself as a domestique for Nibali last year. Feillu might have the better chances, just for being French, and for being famously abnoxious when missing out on the TdF. They will both be up against Linus Gerdemann, who has ridden the most TdF's, but rarely as a domestique, and with unconsistent performances. My personal preference goes to Zaugg for being, IMO, the best domestique and best team player
So my conclusion is:
Absolutely certain: A. Schleck, F. Schleck, Cancellara, Fuglsang, Monfort
Pretty certain: O'Grady
Depending on form: Voigt/Posthuma, Feillu/Zaugg/Gerdemann
Wegmann and Gerdemann might not have the best chances so far, but I hope they will get their chance at the Giro. Wegmann might be a possible wildcard, as well as Dominic Klemme - not this year, but if he can deliver again at Flanders and Roubaix this year, I could see him in a Breschel-esque role in the future.