I think this game is much less about Keenum and much more about the run game. Murray & McKinnon are up against a soft run defense and this has TOP all over it. Vikings defense has no weakness and while folks are pointing to Jaguars as a top defense they can be exposed in the run game. I realize post-Dareus it has gotten better, but the Vikings truly have the best unit on the field today.
Going back to Keenum, the Vikings are not relying on him for points. He put up big numbers here and there but let's not forget the offensive scheme is short, quick decision based routes. They don't need Keenum to sling it and it is the same reason Bradford had success. There is not a ton of pressure on the QB to win the game. That is entirely because of the defense.
All of this said now, it just boils down to what you want to believe will happen. Saints offense beats the Vikings defense or vice versa. I don't think Vikings offense v. Saints defense is the story here meaning who cares about Brees v. Keenum as they don't play directly against each other.
Both teams have comparable rushing attacks in terms of ypg, but Vikings RD is significantly superior here. Shift into the passing game and clearly an advantage to Brees/Saints here but Vikings PD is again far superior to the Saints.
Vikings run v. Saints RD = Vikings
Vikings pass v. Saints PD = Saints
Saints run v. Vikings RD = Vikings
Saints pass v. Vikings PD = Vikings
Not large margins above mind you, but in 3 of the 4 matchups I am giving Vikings the edge. I'm probably not going to play this one necessarily since I have both of their futures from pre-season, but this is what I saw.