Whistler is having an EPIC snow year (606 cm / 19 feet to date!) and that has caused a fair amount of chaos on the Sea to Sky highway due to cars (and drivers) that aren’t prepared for the road conditions.
BC law states that you must have winter tires once you pass the warning signs on the highway just north of Squamish. If you get pulled over then you may face a $109 fine and will likely get turned back. Not a cool way to start your vacation! Unfortunately, almost all rental cars (except some large SUVs) don’t have the appropriate tires to pass this requirement. Even if they did, most all season tires are TERRIBLE in snow. This is especially true of the wet snow that typically falls on the highway to Whistler.
The moral of the story? Unless your car is equipped with winter tires, think twice about driving to Whistler between November and April! It may sound self-serving, but you are probably further ahead to book a whistler airport shuttle or a private transfer.