If you are going to be photographing waterfalls, think about how you are going to get to an exposure of 1 to 3s to blur the water. You probably will need a 3 stop ND filter or maybe 6 stops if working on broad daylight.
If carrying a tripod is not an option, the you can shoot 1/6s to 1/4s hand held with the 24-105mm at 24mm fairly reliably. You may still need a ND filter to do that.
You may want to consider whether it is possible to carry something like a Gorillapod with, otherwise the approach I outlined above of using a wide angle lens with IS will help with photographing waterfalls.
Also think about taking a circular polariser.
I have to admit, I would probably make do with the 24-105 and 17-40. If I could take only one lens it would be the 24-105.
I spent last week in the Grampians and between my wife and myself we had a 5DII, 5DIII, 24-70 II, 24-105, 70-200 IS II, 17-40, 15mm fisheye, 50mm f/1.4 and 100mm L macro. The 24-70 and 24-105 saw most use. After that the 100mm macro and then we took a couple of shots with the 17-40 and 70-200. The fisheye and 50mm did not get used. We used a 3 stop ND for waterfalls and circular PL quite a bit. Our 10 stop ND did not see any use.
I agree with this; when I went, I only shot with the 17-40 & 24-105, but I do realize other people may want to use the 70-200 at times too.
Regarding the hike itself, obviously don't forget to take food and water...and the fact that it'll add more weight. I'd seriously consider the mules or the helicopter, depending on the day you go. I had to argue with my friend for the helicopter. The helicopter was well worth the $ IMO, not only in not having to hike, but since it's about a 5 minute flight that's hours more shooting, not hiking; also saved our legs for the rest of the trip. Once we got there and saw people literally barely able to walk as they climbed out of the canyon coming back, she agreed with me lol. But that all depends on your fitness level of course.