The problem I have is that the Saints are good at everything that burns the Vikings:
They have an outstanding punt/kick returner, and the Vikings are NOTORIOUS for having horrible special teams coverage. Reggie Bush has destroyed the Vikings before, and I expect him to do it again.
The Saints have a very explosive offense, which is the kind of offense that the Vikings struggle most against. The Vikings love to give up big plays, and big plays are what the Saints do best. I'm expecting at least one long pass and one long run, but there could be more.
The Saints' defense is incredibly opportunistic. The Vikings often turn the ball over in pressure situations (such as important games like the NFC Championship game), which could very well lead to a pick 6 by the guy that the Vikings should still have on their team, Darren Sharper.
That being said, if the Vikes want to have any chance at all, they need to put a lot of pressure on Brees. If the defense can play like they did against the Cowboys, then they might have a small chance to win. The offense also needs to be mistake-free, because the Saints will jump on every chance that they get.