We did Wetherspoons one year, sounds like it would be terrible but it was amazing and they made the building look lovely with huge trees, candles etc, £25 each with a few options and a wide choice of dessert- we got a choice of 2 soups with bread, yorkshires, stuffing, roasties, parsnips, mash, peas, carrots, gravy and nutroast or meat option, dessert was a choice of xmas pudding and custard, brownie and ice cream or after eight mint cheesecake with ice cream then coffee and mince pies with brandy butter or pouring cream. It was all really nice.
Alternately a friend went to Britannia hotel Manchester and said that service was slow but the food was ok and tasty, she said it was carvery style so things weren't super hot due to being on the counters but the actually tastes were ok, comparable to toby carvery.
Another friend went to the Hilton on deansgate and had nothing but rave reviews, also i have stayed there in november and the decorations are beautiful. Very expensive at £99 per head but it is only once a year and I have seen worse...
I found a list online and it lists the palace, lowry, san carlo, beef and pudding and red hots prices/menus
www.manchestereveningnews.co.uk/whats-on/food-drink-news/christmas-2015-manchester-restaurants-open-9986651