I floated Dominguez a few years ago in mid May - I remember it being really beautiful, flatwater for the entire trip. We put in at Escalante Creek and took out at Bridgeport, I think. Western Whitewater refers to Dominguez Creek Rapid as II- and mentions a couple of riffles and a diversion wier.
I don't remember any rapids though the flow was about 5K cfs, and any riffles may have been washed out. I've heard folks say that running the entire reach from Delta to Whitewater (there's no whitewater there) takes you through some less pleasant countryside. Much of the land on river left is the Dominguez Canyon Wilderness Study Area so it should be pristine (though there may be drill rigs all over the place these days...).
If you go, make sure to take plenty of time or even a layover day for a long hike up Dominguez Canyon (good campsite), its spectacular and I regret not spending more time there. I found the BLM folks in Grand Junction very helpful - call them and they'll send you info and maps. 970-244-3000.
Another good float that would be good in a canoe would be the White River out in Utah. This offers beautiful scenic canyons.
Have a good trip!
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse