Alaska bound from Calif

Why would you ever cross from the mainland into Vancouver Island?  You didn’t say you were exploring the Island. 
Are you planning on ferrying up from the L48 or driving up?

You can drive from anywhere in the L48 to basically anywhere that has road access in AK without using a ferry. 
And fwiw, most all ferries, including AMHS, WSDOT and BC Ferries all handle semi trucks. You can hitch a ride. You pay by the foot!  

Regarding which roads to avoid?  I’m going to presume you haven’t actually mapped it out. There’s only 1 way up save for whether you take the Alcan or Cassiar through northern BC. 
And AK has like 6 highways and not really 2 different ways to get to the same place except from ANC to FBX. 

If you’re just hatching this plan now and  plan to go in 3 months you must be planning on boondocking the whole way and no substantial reservations.  Otherwise it’s gettin to be too late for a lot of substantial 2025 reservations. 

I drove from Idaho into Canada and to Dawson Creek at the start of the Al Can Highway into Delta Junction Alaska at the end of the Al Can Highway, in May 2023 and it was a fantastic trip.  One of my daughters lives about 1-hour from Denali so I had free parking at her home.  
for me, the driving is the adventure.   It just happens that ferries cost more than fuel and provide less of an adventure.  
and talk about wildlife! Elk, bear, horses, bison, lynx, moose and more.  None of which would be seen on a ferry.   

The road thru Denali had a big slide which closed it.  The only way to “Drive around there” is on a park tour bus.  And of course wildlife stays away from the noise of the buses.   
Talkeetna is a great little town just south of Denali but no large rig parking or driving in it.  

I did video of the entire trip if you want to see what the roads are like.   Click the link: 
https://youtube.com/playlist?list=PLtt6guwxkjvHNXy5WeTIuGpkrYJhIA4iQ&si=0MTeF-yB63_O06fB

yes you can cross the ferry with the 5th wheel from Vancouver Canada to Victoria, I don't know if the one out of Bellingham I think it is allows rv's or not.  just look up the ferries and cheek it out.  it does get very expensive taking a trailer on bc ferries though.  I lived in Victoria for 20 years and never took the trailer off the island until I retired from the navy and they paid the bill for my final move.  prices have gone up yet again, so my truck and 5th wheel is 56 feet long.  it costs 19.10/persona over the age of 12, it is 67.40 for the first 20 feet of car/truck and then 7.50/foot over that so for myself the wife and my setup it is 443.1 each way on the ferry.  Oh and add 20 bucks for the reservation.  its smart to get one in the summers or if you can't afford to wait a few sailings or even till the next day when it is real busy.

now on the BC ferries they do have fare savers and specials on the lesser used routes where you can save some money.   in the summer they usually have a "size up the savings" or something like that where the excess length on certain sailings is about 50% of the regular 7.50/foot.  you just got to go on the web page and look as it gets closer.  

you could take a ferry to the island from Tsawwassen (Vancouver) to Swartz bay (Victoria) then when you leave you could go from Nanaimo to horseshoe bay (Vancouver). 

Go to their website. You book in advance and provide your total length. Everything you need to know.

https://www.bcferries.com/