Generally in-town temps are between -5 and -15 degrees Celsius throughout the winter. that being said, there is always a 2-week cold snap where it dips down to -33 (or -42 like last year... damn). Hope it's not the week you're there! lol
But really, on-hill you're looking at about -8 to -20 Celsius normally.
Typically, I was riding with a thin undershirt, a hoodie, and a windbreaker style shell. This worked on 90% of days, only 3 times did I wear my parka. I usually rode with longjohns under my snowpants (thin insulated) and the vents always got cracked open after the first run.
You'll find the runs fine. The thing that'll freeze you is the chair lifts. High altitude (sunshine is 7000ft base elevation) so there's quite a bit of terrain above treeline. You are completely exposed on some of the lifts so you will freeze! I find it a lot more mild compared to Saskatchewan or Northern Quebec. Definitely colder than BC though.
Probably similar to Montana/Wyoming if you've been there in winter.