For a while it looked like a Catholic nominee was most likely between Christie, Rubio, and Ryan as top contenders. All have been removed somewhat or completely in the past year.
Midwest yes, but the problem for the GOP in the midwest is catholic and secular working class voters. The ones who are most religious most likely voted for Romney because of cultural issues, but such has less play for those who aren't as religious.
Nationwide, Romney got the same percentage of Evenglicals as Bush did in 2004 (78%) and they comprised a higher percentage of the electorate (26% versus 23%) in 2012 then they did in 2004.
I thought Rubio was Mormon?
He goes to Catholic and Baptist churches. Not sure which one he or his wife belongs to personally.