Throughout the movie, Hans Landa was always a step ahead of the motives and plans against the Basterds. Even in "Operation Kino" after he so intelligently deduced the German movie star was the double agent against the "Third Reich" he killed her during the movie premiere of "Nation's Pride". He could very well spoiled the actions of the Basterds then by imprisoning Aldo Raine and his associates. But he didn't.
He let the other two guys from the Basterds execute their plans to blow up the theatre. Was Landa planning it all along? Or was it just an instinctive decision on his side to choose the side of Basterds on seeing a way to end the war? This is not quite clear considering his reputation serving Germany for all those years.