Not a Sitka guy but I fished a bit down the coast a LOT (too much perhaps)
That time of year you will have great king salmon and halibut, lingcod etc with your friends out on the saltchuck. Kings are challenging but can be had and will succumb to a deep sunk fly raised with the drift. I have landed kings in the 30# class on a fly. Some have landed huge halibut on flies out in that area but it's probably not too practical.
The coho salmon out there will blow your mind out on the salt the way they hit, jump and run. They love flies too if the captain will let you fling flies out there. Just look for them feeding on the surface or drag a bucktail in the propwash (yes right in the propwash) while the rest are trolling and hang on tight!
Inland the native rainbows and summer steelhead should be peaking, I hear they peak April - June there you lucky dog. Nothing like a hot summer run on a flyrod.
Also sockeye run in June. The river should be alive with activity.
Alaska is synonymous with insane fishing I think you guys will have a blast and also in for some fine eatin' too! Dungeness crab, fresh halibut and wild salmon on an alder coal fire with a blackberry cobbler (might be too early up there).
Take pics and please post a report!
(others from the area may chime in with more localized info)