take this topic to the main boaters forum and you'll get a lot more responses. In Colorado there is a ton of 3-4 stuff. Some of the main runs in May would be the Poudre, The Arkansas: Brown's Canyon, Royal Gorge, Granite down thru Numbers (Would need to walk one 5), Roaring Fork just to name a few. This is a really huge question. You might want to at least focus on certain states. If you are going to head to canada, you should boat in Washington, Idaho is good to hit on the way to washington, Montana into Idaho going over lolo pass would be another stop. You should check out the book that is supposed to be out this spring that is a comprehensive guide to many western states.