If Wisconsin goes 11-1 this season, they will be in a BCS game. You're getting a little bit too far out there with your hypotheticals. That's the reality.
Actually you might be getting a little ahead of yourself assuming an 11-1 Bucky team would be in a BCS bowl game in the hypothetical given here (12-0 MSU, 11-1 OSU/Wis).
That will put MSU in either 1) the Rose Bowl or 2) the national title game.
If MSU goes to the Rose Bowl, then that will leave the individual BCS bowl games to determine if they want OSU or Wis as an at-large. Depending on matchups, it could be OSU. That would leave 11-1 Wis out.
If MSU goes to the National Title Game, then the Rose Bowl MUST select a non-BCS automatic qualifier should there be one. This is a new rule. If that's the case, then TCU/Boise State would likely be in the Rose Bowl instead of a Big Ten team. The matter gets further muddied should Oregon be in the National Title game, too, meaning the Rose Bowl lost both their automatic teams. Then, the Rose Bowl MUST take TCU/Boise State if either is an automatic qualifier. Then, they get a second selection and I believe OSU becomes a more attractive alternative as the matchup against TCU/BSU than would Stanford or Wis (the other options, IMO). That, too, could leave 11-1 Wis out.
Could a BSC bowl choose Wis over OSU? Sure. But, it seems more likely that Wis would be chosen behind OSU in most at-large scenarios. OSU is an enticing matchup for most of these high-level bowl games.