if your hiring straight from the airport consider getting a cab to just outside the airport where we found a few hire firms(the same companies that are based in the airport),their depots are based here and a whole lot cheaper than the airport desk.
you'll just have to check if there is an office in whistler though as we used enterprise but they don't have an office in whistler so we had to have it for the week.
from the airport, getting through the city and the drive to whistler(stopping to grab a coffee from squamish etc) will take 2.5-3 hours.
there is a train upto whistler, you could try that.