I would highly recommend going out of Erie as opposed to Dunkirk. There tend to be more 'eyes in my opinion off Erie in late summer and the ridiculous amounts of steelhead that PA stocks results in a phenomenal mixed bag offshore fishery in August. I hope he isn't looking to go the first weekend in August though because there is a big tourney out of Erie that weekend and most charters participate.
I would HIGHLY recommend Vision Quest Charters (Capt. Pete Alex) he wrote an article in "Great Lakes Angler" magazine last month about the Erie offshore fishery and is a good friend of mine. If you get a chance to check out the magazine article, the blurbs by the magazine editor (who has fished with me and with Pete a few times) at the end will be all you need to know about his impressive resume on Lakes Erie and Ontario. He is a phenomenal captain, with two beautiful fishing machines (a 28' Tiara and a 36' Tiara), and catches boatloads of fish including a 21# King Salmon last August off Erie!