Thirded. I love Supernatural. I think Jared fits the physical description and age perfectly, I just don't think Padalecki can pull off the snarky Harry Dresden persona.
You'll never know if you knock him down without finding out. Give him a chance to broaden his acting spectrum a little. He's gonna surprise all of you in the upcoming 6th season of SPN, I guarantee it.
And though I agree with Denisof (in theory) he is too old now to actually play Harry.
I love Denisof as well, though I believe I agree with you in that he's kind of passed the mark of when playing Harry would have sky-rocketed him. Maybe had they come to him with the idea of a Dresden movie just after finishing Angel, it might have made more sense. If all else fails, Alexis can play Malcolm Dresden in Harry's flashbacks.
Hugh Jackman might make a good Michael...though I like Viggo Mortensen or Sean Bean more.
I pick Viggo as Michael. I adore Hugh Jackman, and I love, love, love Sean Bean, but I think Viggo hits the nail on the head as far as the character f Michael goes. It is something in Viggo's voice that cements the foundation of Michael, the idea that one man can be so utterly good, so utterly encompassing of every characteristic of a man devoted to his family and his work and his faith that just defines what Michael can be. Go read Aragorn's speeches from the Lord of The Rings and TRY and tell me that some of that doesn't sound like Michael (particularly the speech that Aragorn gives as the Rohirrim and the men of Gondor prepare to attack the Black Gates of Mordor).
Eric Roberts as Marcone would work, though I feel like Eric Roberts would be really cliche considering he has played that same type of character many times. I kind of think Bruce Greenwood would make an ok Marcone, though I think there is probably a better choice. Robert Knepper who I suggested for Nicodemus could probably pull of Marcone too.
I'm still all for Ray Wise as Marcone, but if you're looking for someone a little younger, why not Bruce Campbell? (and yes, it was your suggestion of Bruce Greenwood -- and the name Bruce -- that made me think of that).