How do I get from Horseshoe Bay Ferry Terminal to Whistler in the winter?
You'll likely have to take the city bus from Horseshoe Bay into downtown Vancouver and then pick up a coach there to Whistler. It'll involve a bit of backtracking, but I don't think there's a way to get from Horseshoe Bay to Whistler, unless you're willing to fork out money for a taxi, but that'll be pricey.
I think Greyhound bus may do this route..but possibly only in the summer??? They show Horseshoe Bay as a stop but a check shows no service for this week.
There is a Greyhound Coach that picks up outside the Horseshoe Bay ferry terminal, southbound at 12h40 pm. You then go to Pacific Central Station in Vancouver where you then transfer to a Greyhound which departs at 2h30 pm. It basically backtracks to Horseshoe Bay but drives right on by to Whistler, arriving at 5 pm.
You would have to purchase a ticket for all this online so that they can alert the driver that there is a pax to be picked up in HB. Greyhound has an abysmal record for customer service in Canada, so I would suggest you take the #257 Vancouver Express public transit bus into Vancouver for about an hour. You'd want to get off at either Burrard (to walk 100 metres to Burrard Station) or Granville St (to walk 200 metres to Granville Station) to take Skytrain to Main St Station and Pacific Central Station. There, you could buy a ticket in person for a Greyhound to Whistler. This would be much more secure than buying an e-ticket from Greyhound for a HB pick up.
You could also look at taking Epic Rides to Whistler after taking public transit into the city. The cost is very reasonable but no wifi and no onboard toilets.
To take the #257 bus, you would buy your Compass Ticket at the Compass Vending Machines at the foot of the escalator at the exit doors from the HB terminal. Epic Rides picks up at Burrard Station, on Melville St outside the back door to the Hyatt Hotel. There would be several coaches, shuttles there, so keep an eye out.