Whistler/Blackcomb is usually the first to open in B.C.
I once skied opening day at Blackcomb on Nov. 13, with 4 or 5 lifts open on the upper mountain and about 5,000 locals. Singles line ups were 15-25 minutes all day and everyone that I shared a chairlift ride was from Whistler or Pemberton, no one from Vancouver. It snowed a few inches of heavy snow overnight with about 1,000 skiers and no lift lines the next day.
Most of the B.C. Interior opens by the end of the first week of Dec., most seasons.
Sun Peaks is able to push their opening day usually to the week before U.S. Thanksgiving due to some snow making but mostly due to 20+ years of summer grooming: no waiting for stumps to be covered because they have all been pulled, rocks picked and dynamited, weeds and small regen conifers cut, grass planted. Early season SP can have a base that is 50cm thinner than other B.C. mountains and still have equal or better coverage.
Sun Peaks offers free skiing the Friday of U.S Thanksgiving weekend for residents of Washington. I don't think that very many, if any, skiers take the 6 hour drive for limited skiing unless they have a place at SP and those folks usually have a season pass.
The first Monday in Dec. is Toonie Day at Sun Peaks for Kamloops residents. A $2 coin called a Toonie or a Food Bank donation is all it costs to go skiing. Every high school in Kamloops closes, every rental ski is rented out and 70s gear owned by one-day/year skiers abounds. It is a for real gaper day and is known by the locals as Body-Pack the Hill Day.
Snow making on the mid mountain OSV race training run usually allows Sun Peaks to have race camps in early and mid Nov. prior to opening to the public.