My only advice would be to not travel past Whistler and climb the hill up from Pemberton. It is very steep, twisty, and narrow. It would help to know your entry point into BC. It would also be good to know your plans and budget. We just came home from California last week, and went to the coast at Arcata. We had a lovely trip up through Oregon, and the west coast of Washington, then took the Coho ferry to Victoria and came home. If you have time and money, take the ferry to Vancouver Island, then take the ferry from Port Hardy to Prince Rupert and drive to Alaska from there. Spend a few days on Vancouver Island either seeing BC's capital city and it's sights, or drive to the wild west coast and enjoy Tofino and Long Beach.
If that doesn't suit you, take the Fraser Canyon route and drive north to Fort St John and beyond. Yet again, go to the Okanagan and cross into Canada there and drive up back Kamloops and Blue River.
None of the highways are anywhere near as steep as the route past Whistler.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel