Bear spray should be adequate. The bears generally are pretty focused on their fishing when around rivers, etc. so they won't bother you. Besides, you would need a pretty high-powered gun to be any good against a 1500lb brown bear (yep, they grow 'em big up there!). If you're smart about how you behave, you should not have any issues.
As far as the other questions you posed, be prepared for significantly wet weather - this is not a good trip for any "sort-of waterproof" gear. You will get wet. The Tongass is a rain forest.
The salmon that have run up the rivers are no longer the healthy pink salmon that you are used to seeing. You could practically walk from one side of a stream to the other on the backs of fish, they will be so dense in some areas, but as they work their way up stream to spawn they are burning off alot of the oils and nutrients that make them so tasty. If you watch the bears, they'll often just bite off the heads (and the stomachs of the females) b/c the fish are so abundant that it's more nutritionally efficient for them to eat that way. The salmon you are used to getting at the store are caught before they even make it into the streams, so they look/taste different than what you'd find upstream. I'm not saying that you can't possibly eat them, just be prepared for what you'll see.
Most of all, enjoy yourself! Alaska is one of the most beautiful places on the planet - you'll have a great time!