My family & I intend to visit France from December 12-24. In addition to Paris, we would like to visit either Annecy or Alsace. I presume we can do half justice only to one another place is addition to Paris. As it is Christmas season, which amongst Annecy or Alsace would be the best to spend time in and how many days? Festive season, heritage, local culture, tradition ,food and nature is our travel interest always not sport activities.Please suggest good places to stay and travel mode. Thankyou for all inputs.

Sounds as if you need to do some research. This forum is all about tweaking plans once they have been established.
Accommodation can be found on the likes of Booking.com or airbnb.
Transportation depends much on where you are and where you need to get too.
I prefer a car. However if you are in the mountains and the weather is poor this will become a bourdon.

My husband and I spent several days in a Strasbourg (Alsace) in December 2016. We loved it! Lots of Christmas markets and a very walkable town. We drove from Paris but you can easily take a train. I would suggest 3 or 4 days in Strasbourg and the rest of the time in Paris. Or, if you rent a car, then do a week in each area, exploring the wine route in the Alsace. Lots of cute villages to see. As long as the weather isn’t snowy it’s easy to drive. No need for a car in Paris.

You’re only a few weeks out, you should probably be booking hotels very soon.

Agree with Tracilee. Been to Strasbourg a few times, usually by train from Paris. In Dec 15 spent a few days there to take in the Xmas markets. Absolutely wonderful! Not far away to the south is Colmar, which is smaller but probably as festive, though we have not been there during the Xmas season. May be a little late to make hotel reservations, but I would definitely try. Been to Annecy twice, but only in the late Spring. Great setting on the lake (surrounded by mountains, of course); nice "old town" area with canals. Snow much more likely there. Don't know if that would be a plus or minus for you. If it were me, I would choose Strasbourg/Colmar, especially in Dec.

I'd do Strasbourg and Colmar. Actually I love Alsace and would do far more but you have very limited time.

Old Strasbourg is very pretty with a lovely area around the cathedral and the older canals. Colmar is an easy hike by train and is smaller and probably not as pretty pretty but has two of three nice squares and again a small canal. Nearby (so a very quick taxi trip) is Eguisheim (other villages exist) with an ancient church and three rings of houses with a high street (a bit touristy) but once off the high street very very french and lovely. With walks in the vinyards freely available the town also offers wine tastings (paid or buy something).

If you follow my name back to 2016 Septemberish you'll see my last visit report from there with some tasting ideas.

Accommodations can be hard to find in Strasbourg during the Christmas season.

I've never been to Alsace for holiday in winter. We always go where weather is better than where we live, so we end up on the French Riviera. 4 hours by train from Paris compared to 1h30 (?) for Strasbourg. Warm weather, we can have barbecue on the terrace.
Now we have all the opportunity we want to go to Alsace whenever we want.
(Same for Annecy where I don't remember having been.)

Christmas in Annecy info

https://www.ifalpes.com/blog/christm...lps-in-annecy/

Last time I was in Annecy was just before Christmas. All of the decorations were up but had not yet been turned on. Nevertheless I very much enjoyed my time there.

Annecy in November | Any Port in a Storm

Thank you very much for all your guidance ! It's really helpful