Colorado is basically guaranteed. They are a huge draw this year and will be the highest ranked and definitely biggest draw from among the other former PAC 12 teams from which the Alamo Bowl can select.
From the B12 side, it's possible that the Alamo Bowl could go for the Colorado-ASU matchup if Iowa State wins the Big 12 championship...but, expect them to select BYU regardless of who wins the B12 championship.