To nobody’s surprise, and to the relief of the “American Idol” executives, it will be Crystal Bowersox and Lee Dewyze singing in the finale next week. It’s hard to argue with the results. Bowersox has been strong all season long, and Dewyze has emerged over the past month to join her as a favorite. The contrast between the indie coffeehouse artist and the paint-store rocker — and believe me, you’ll hear that story line a zillion times this week — will be fun to watch.