On the replays admittedly Bennett does raise his right arm and his gloved fist may make contact with Marchand’s head. However:
1) Marchand initiated the contact (he was aiming to hit Bennett who was only intending to dump the puck and then get a line change).
2) Bennett had to prepare for a hit, knowing Marchand may have been looking for an opportunity to test his left hand (yeah, he’s equally dirty and would hit the injured hand if he got a chance).
3) Part of preparation was to protect the left hand and thus extend the right arm.
4) If that happened to connect with a significant punch to Marchand’s head, it most certainly wasn’t a sucker punch. I would congratulate Benny for the lightning fast ninja reflex and remind anyone wishing to sucker check a player who’s trying to dump the puck to not be unprepared for a counter hit.
5) The whole sequence is Marchand’s own fault.