Re: Colorado River
Dunno for sure, but the timing may be right to catch a white bass run up the Colorado from Lake mead. Come to think of it, might be whites/sandies and Stripers as well. Light colored baitfish patterns fished near the bottom will be the ticket there. Most white bass can be handled on anything down to a 4wt, but a 9wt wouldn't be overkill for the stripers. If you're gonna take one rod, I would want it to be a 6wt or heavier.
On the first part of your trip, closer to the main part of the grand canyon, I think you might have some chances for trout. Some of the residents of the area will know better and I'll let them cover that fer ya.
Take plenty of gear to stay warm too, the nights will sure be cold.