Well it appears my guess (see this post) was way off.
Variety has just posted this:
Marisa Tomei and musician Josh Groban have joined the cast of the Steve Carell-Ryan Gosling marital crisis comedy for Warner Bros.
Story centers on a father whose life unravels while he deals with spousal problems and tries to manage his relationship with his children. Annaleigh Tipton ("America's Next Top Model") and Emma Stone have already been cast.
Tomei will play the first woman that Carell's character dates after he's been schooled by Gosling's character in the art of meeting women. Groban will play the boyfriend of Stone's character.
Pic's produced by Carell under his Carousel banner and by Denise Di Novi. Charlie Hartsock and Vance DeGeneres are exec producing.
John Requa and Glenn Ficarra will direct from Dan Fogelman's script.