OK, so I just spoke to a customer agent on the 1888andsoon line and he told me I just need a voucher and can then book whatever room I want with W or in this case Westin Whistler (classifies as W in AIR MILES).
This is splendid, and as I understood him, I can book a $869 room and use the vouchers with it.

Do anyone know anything else that I should be aware of?