I still think Jackson could pull it off (would have to be a shaved-head Jesus). Morgan Freeman is so good at everything he does that he could probably pull it off...I just can't imagine him young (but he has gravitas in spades). Also, Freeman has already played God quite believably in Bruce Almighty.
I liked Freeman's God better than George Burns' God, but both were good.
The shaved head is something hard for some to swallow, but seeing Lou Gossett, Jr in Officer and Gentleman got me thinking of him in that light.