Stone37, I don't think that's right. The trigger for Bossk's ability is when his attack hits. The very rule you quoted says that we cancel dice results and only then can we say that the attack hit or missed.
With an autoblaster we might roll a (hit) and know before that moment that the outcome will be a hit. Bossk's ability still won't kick in until the very end of step 6, after the defender has had all opportunities to cancel any (crit) results. Autoblaster is a bad choice for Bossk.