Wool, layers, and some kind of snow suit or snowmobile type cover are highly recommend. Mittens-2 pair, or some way to layer hand protection. You'll want some work gloves to handle the dogs. Boots made to wear outdoors for several hours and still have warm feet. Mukluks, sorels big enough for extra socks, or similar.
Many extras are available at the cabin.
Sleeping bags are provided for those sleeping in the loft, there are 2 double beds for the rest of us. The cabin is woodstove heated, lit by lantern, and the outhouse is 'solar' heated. An opportunity to really get away. A packing list will be sent when you register. Meals will be provided by Janice and prepared by all.