Hi, Bharti!
It doesn't experience much snowfall during December. So, the roads are clear and views are amazing. Just that it gets a little too cold in Dalhousie and the minimum temperatures can drop to as low as -5 degree Celsius. If you are fine with it, it's definitely a great idea to visit Dalhousie during Christmas.
Would you like to join us we're going to Dalhousie too in December. 26th-30th December if you're a couple it would cost you around 6k per person with cab for sightseeing and budget hotel