At the present time, all indications seem to be that Verlander is the favorite to be the #5 starter at the beginning of the season. Roman Colon has a good shot at it as well. Zumaya is unlikely to get it, but he'll be making his bid too. Leyland and the papers are saying Jason Grilli is in the mix too, but I think those rumors will be negated when they see him pitch more.
Contrary to many Tiger fans, I'd like to see Colon get the job if he pitches well in ST. He has the stuff to be a pretty decent starter, but the results have been a bit spotty so far. Let Verlander and Zumaya mow down AAA hitters for a while to get a little more seasoning.
If they go Colon or Verlander, it's an upgrade over Sean Douglass and a hurt Wil Ledezma, our #5 starters from last year.