Fished the upper river last week and it was awesome! Started at Vallie Bridge, went to Rincon, and kept moving west from there. Pulled some very nice browns in the 17 inch class, plus one toad of a rainbow!
Fly fished the upper river and used a scary creation of mine called a Dark Prince. The water was cold enough to numb your legs through two pairs of thermals and waders, but not unbearably cold. This trip was during good weather a week ago, before this current front hit. Air temps were in the mid 60s. I would tell you where it was exactly, but some secrets are meant to be kept!
As long as there are no ice bergs floating down the river, the area up near Buena Vista should be fishing good. It's gonna be dicey over the next week or so because they got hammered by snow and it was cold up there last week. If you want to catch numbers of fish, start at Parkdale, which is just west of Canon, and move up from there. There's a ton of access all along the river - just pay attention to the signs. Mid morning bites are generally best in the canyon at this time of year because it takes a while for the sun to hit the water and for things to start moving around.