The steelies are some of the strongest fighting fish, out there. They're a blast, when hooked in rivers like the Salmon because of the flows and the size river it is.
A guide would be helpful, but not necessary. There's 12 miles of public access on the river and most places are clearly marked. There's two fly only zones but they have seasonal use times, so you'd have to check the regs, to see which would be open at the time you'd plan on going. About the only place you'd be able to use your canoe, would be down in the estuary, so i'd probably leave it at home, especially if the flows are up. It's definitely a wadable river, so a boat isn't necessary.
An 8wt. is good for the steelies in there. I prefer 10 footers or two handers but a 9' will work fine. As was mentioned, flies like buggers, esl's, egg patterns and stonefly nymphs, usually work best. Estasz is a popular material for patterns on the Salmon. As was also stated, studs, cleats, korkers etc.., are all not only practical but necessary, at times. The river bed is typical freestone, but there some of the most awkward, slippery rocks, you'll ever walk on.
As far as times go, winter and spring are the best times for steelies on the salmon. There can be good numbers in the fall, but your looking at big crowds (of some of the most questionable people you'll ever see), chasing the kings (literally) up and down the river. The crowds are pretty much gone after the kings, so anytime after that would be good.
For more info:
salmoncrazy.com, Whitakers Fly Shop, Yankee Fly Shop and Fat Nancy's.