Scott Walker.
Too squishy on illegal aliens for my taste.
That being said, the American sheeple have been dumbed down to the point where a white male would be unelectable against the latest group novelty. It is all about identity politics now.
Marco Rubio has that, but so does Ted Cruz. Plus Cruz has some GOPe credentials (Harvard graduate, looks presidential, very intelligent and well spoken) that the GOPe could swallow hard and get used to him a lot easier than we could to a squish like Rubio.
The GOPe would never go for Walker or Cruz.