Much has been made of his winning 3 elections in Wisconsin. Well, 2 of the 3 were midterms and the third was a special election against a candidate that wasn't willing to repeal the law that Walker's recall was about. Wisconsin is much more blue in Presidential years and early polling in Wisconsin suggests Walker would start out a slight underdog against Clinton in his home state of Wisconsin.
Walker will also have to make it through a crowded GOP field which includes Bush, Trump, Rubio, Carson and Cruz all at the top of the field right now.
Walker trails by 8.4% on Clinton over the past 7 national polls. This extrapolates to a 347-191 electoral vote victory for Clinton. This would put her within striking distance (within 4%) in Arizona, Indiana, Missouri, and Montana. She would carry all 2012 Obama states plus North Carolina. She would be a little over 4% down in South Carolina. While things could very well tighten up here, Walker has an uphil climb if he wants to win the GOP nomination and then the general election.