I'd bench Halladay. Then again, I'm a more conservative manager as I bench all pitchers who go up against the Yankees. However, I don't kick and punch myself when the benched pitcher does really good.
With that said, Mussina's career numbers against the Bluejays aren't bad at all. If he does well, I think he may pitch 7 or even 8 innings as the bullpen needs rest after last night.