Hello.
I have just checked around, and it looks like you may find what you are looking for at the Chateau Frontenac.
Here is a link to their website. On the botton right of the homepage you will see a section called Christmas Celebrations and it has all the information there.
http://www.fairmont.com/frontenac/?cm_mmc=icppc-_-Chateau+Frontenac-_-google-_-chateau+frontenac
It would be the perfect spot for Christmas in every way. It is absolutely gorgeous.
Also, Besides Panache which I recommended earlier this evening, another restaurant is Toast. It is a small restaurant with great food and service. I am not certain about their Christmas hours although I know they were open on Thanksgiving Day. I am sure a quick email or phone call could answer your questions.
http://www.restauranttoast.com/en.htm
Hope this helps a little. Best of luck!
n/d