Previously when the Saints and the Lions met, The Saints defeated them 31-17. It was a pretty clean game, with the exception of the Lions missing two field goals, so there isn't a ton of wiggle room in determining if the Lions played poorly or if the Saints are simply that much better.
One thing I look at is that in that game, Stafford passed for more yards than Brees. If he can do that again, with the way the Lions have been playing lately, winning three of four with that only loss coming narrowly to Green Bay, I can't see them losing by more than a touchdown if they lose at all.
I'm thinking that it will be a game very similar to when they played Green Bay last week, a back and forth shootout where no team really is able to separate itself by more than a touchdown. If that holds true, then Detroit should cover easily.
I don't think that Detroit should be picked to win straight up this week, even though the odds for it are pretty good. Their defense simply has been playing too weak for their to be enough confidence to make that pick. Unless Suh and Fairley play ridiculously well, I can't see Detroit beating New Orleans, but they should cover with ease.