Sedona does not get dumped on with snow that time of year or really anytime. It can, and does snow there, and I would be prepared just in case.
Plentiful hiking trails around the Sedona area and AZ in general. Do some!! Check out a book from the library entitled 100 top hikes in AZ. In December, desert hikes are also doable and spectacular. One of the things I miss the most about AZ is the hiking and the wide variety of trails to hike and different types of hikes from desert to tundra.
The Oak Creek Canyon drive from Sedona to Flagstaff is rated one of the Top 10 drives in the US by Rand McNally. I did it several times when I lived out there and it was never the same. I did it once in December and yes there was snow on tops of the red rocks around Sedona and it got a little snow covered when we got close to Flagstaff, but the drive is unbelievable.
The Grand Canyon should be a must. Again, some hiking down into the canyon in December is doable and well worth it. There is a Native American sunrise ceremony (I believe Hualupai but not 100% on that since I am 13 years removed from AZ) once a week at the Grand Canyon, on their land, that anyone can attend. I happened to attend one and it was indescribable in its reverance, beauty, and spirituality.
I doubt that Snow Bowl in Flag will be open. I did ski Snow Bowl once in December when we lived out there but I think that was not the norm.