Tim,I've done a few river floats(nothing with realy rough water and waterfalls that big).I have done the feather,taking out just past the outlet from oroville.That was the worst rough water I've had it in and it handled it just fine.(20-25' roostertail coming into the river)The worst part of it was getting pelted by the ahole salmnon guys chucking lead wieghts at me.I have a outdoor eng versa vessal and I can say they are very stable in the water and are great for rivers.
I do know someone who uses their kickboat for running white water(up to class 5 rapids)He makes his own boats and have seen pictures where I thought he was insane.I think th pontoon boat would be much more stable than a canoe.If the current isn't too strong then it's not a problem to stay in one spot while fishing. A few of us do float the merced,tuolome and mokolome rivers for smallies.It's a b;aslt and you can get a ton of fish.
Hope this helps,Swampy