I could be wrong but I really don’t see this as being that likely of a match-up; it is certainly possible, and Romney is probably the frontrunner of known possible candidates, but I really think that it is possible that an outsider could come out of nowhere and get the Republican candidacy.
While I think he is too inexperienced to be a successful candidate for president, and I suspect he probably has a lot of skeletons in his closet that would prevent his run, I do think that the Republicans may be looking for someone like Scott Brown for the 2012 election. Basically, someone who is good enough looking and a strong enough speaker/debater to go toe-to-toe with Obama in a televised debate; and still being a man of the people with a populist message that can attract the independent voters without alienating the conservative base.
Personally, I think that Bobby Jindal is a more likely candidate that Romney ...