Hard to go wrong in that area...while I don't know much about right at Port McNeil, I mostly fish north side of Malcolm Island and the Mitchell Bay area. July/August is always prime for salmon 20-40 pounds off all the north points and north corner of Donegal Head with Lizard and Malcolm Point the best (
http://www.northislandtours.com/sointula_map.htm).
Fishing 40-60 feet in 100-120' of water usually works well. There have also been real big ones caught right in Mitchell Bay itself - several in the 40's, and a couple in the 50's last time I was there.
August/September gets just stupid for coho - mostly off the kelp beds along Mitchell Bay. Double/triple headers the norm....
Haven't been for 2 years, but our July trip, we caught several springs 20-25 pounds, and then late August (I think), alone in my boat I probably caught about 15 coho over the weekend. Several double headers and even one jumping right in the boat! As for halibut - I know it's really good as well, although I'm not sure of the main area (think north side somewhere) - only place I've fished is in the middle of Cormorant Channel level with the end of Meynall Road on Malcolm - halibut up to 100 pounds, and the only time I fished it we caught a 30 and a 40....
Just watch for the Sund Lodge boats and they tell you where the action is. They usually frequent Lizard, or Blackfish Sound/Baronet Passage/Hanson Island area, and finish up at Mitchell unless its coho time in which case they often start there.
Really can't go wrong from June to September unless you are looking for shorts weather - far and few between!
I MAY get up there at the end of the month - will post a report if I do.