Tough to say. I suspect that most of the usual must-see suspects (Crooked Stave, Comrade, etc.) will be open, but hours will likely vary from normal and you'd be wise to check with each specific brewery that you want to visit. Do a quick search of this forum to get a good list of breweries to visit.
I was in Alpine Dog 2x this weekend and if I understand correctly they are closed Christmas Eve but open on Christmas Day, maybe with somewhat limited hours. You might check the website for better info than this! This brewery got sort of short shrift in the epic multi page New Colorado Breweries thread but I liked it as significantly better than average immediately and it is even better than that now. Colfax Gold, the Belgian pale, seems drier than before (a plus IMO) and the IPA and DIPA that I had were excellent examples of the style.
Awesome! I'll be there both days as I have no Xmas obligations. What are your hours going to be on those days?
Denver is a city full of (the good kind of) transients. You'll be surprised how many places are open on major holidays.
I'll be brewery hopping on South Broadway tomorrow with my friend and his gf. Starting at Declaration and working our way north: Grandmas House>Former Future>Trve and I'll be ending the night at 3 Kings (not a brewery, I know).