According to this source, Toby Jones will be playing Calculus.
According to IMDB, he's playing Aristides Silk, the pick-pocket, so who can say at this stage? So far I think the most likely suggestion is jock123's that Calculus will be one of the scientists involved in the Inca expedition, which unfortunately would probably mean no shark submarine - something I for one will sorely miss.
The IMDB cast list also mentions a 'Market Artist'. If this isn't a cameo appearance by Hergé I'll be very disappointed!
On a different note, I find it interesting that this film will be structured like none of the previous Tintin films - it's the first one not in French & therefore doesn't presume prior knowledge of the characters. I suppose this freed up the writers & Spielberg to make a film that stands alone, rather than relying on the viewers already being familiar with the books, & also gave them more license to cherry-pick bits from other books to make a cohesive story.Edit:
Sorry Rianna, cross-posted!