The Kenai pretty much has four floats: Kenai Lake- Sportsman's (Upper), Sportsman's-Jim's Landing/Russian (Refuge), Jim's-Skilak Lake Upper Landing (Canyon) and Lower-Skilak Lake Landing-Bings Landing (Middle Float). The first three are non motorized float only with the exception of the first quarter mile below Kenai Lake. The fourth float is a motorized drift area. Here is a link to the fishing regs for the Kenai. Besure to check out the Emergency Orders on ADF&G's website before fishing. http://www.adfg.alaska.gov/static/regulations/fishregulations/PDFs/southcentral/2015SCkenairiver.pdf. From Skilak Lake to Kenai Lake is all single hook, no bait allowed. See the Method and Means in the regulations.
As far as the float go, both the Upper and Refuge floats are fairly easy with mild rapids...maybe a class two on the upper. The biggest obsticles would be sweepers. The Middle is even milder as far as difficulty goes than the Upper and Refuge. The biggest problem with the middle is that you have to motor/row quite a ways to reach the river. If it is windy, then Skilak Lake can get really rough and choppy. The Canyon float is the hardest and most technical float and is not recommended for anglers with little rowing and white water experience. There are class III and IV rapids in the Canyon. The Canyon float is also great affected by wind and should not be done if the wind is predicted to blow up.
We hope that this is helpful.