Late July and August are ideal times to tour in British Columbia and Alberta.
You could ride north on Vancouver Island, take the ferry to Prince Rupert,
Then do a large loop to Jasper, Banff, and down to Glacier NP in Montana.
This would include both the spectacular Icefields Parkway and Going to the Sun Road.
Then you could take Amtrak back to Seattle & Vancouver. (If you are flying out of Vancouver, too)https://www.crazyguyonabike.com/doc/page/?o=1&page_id=26464&v=NS
If you work your way backwards in this journal, you can trace the route exactly.
You would start by taking BC Ferries over to Nanaimo - lovely way to begin a big trip.
The southern half of Vancover Island has plenty of services - northern of Campbell River they get slim.
The day ferry thru the Inside Passage is fabulous - nice hostel in Prince Rupert - but make reservations.
The ride along the Skeena River is primieval - such a powerful river ringed by huge mountains.
Make sure to take in First Nations cultures - especially just off the route in Hazleton - Ksan village.
The stretch of Hwy 16 between Houston and Prince George is pretty uneventful - rolling - fast riding.
It does get pretty empty between Purden Lake and McBride - but then you hit the Rockies.
Do not - I repeat do not - skip Mount Robson Provincial Park.
You can cycle in to a backcountry campsite on Kinney Lake - awesome.
Then its off to Jasper - lovely town - and the Icefields Parkway.
Take your time - you will have plenty of time for this loop.
So spend an extra day here and there and do some hiking.
There are a number of fire roads that you can use to access backcountry sites.
From Canmore, ride down to Kananaskis and over Highwood Pass.
Then its down to Pincher Creek and Waterton Lakes.
Finally you can cross into the U.S. and Glciaer Park.
Many Glacier is the best area for hiking - unbelievably beautiful.
For dessert - you have Going to the Sun Road - one of the best rides in the world.
You have plenty of time to get to Whitefish and catch Amtrak back.
Or, if you are ahead of things you can ride the Northern Tier all or part way to Anacortes.https://www.crazyguyonabike.com/doc/?o=1&doc_id=2937&v=Bx
Other than Whitefish, the only other baggage station is Spokane.
Feel free to ask me any questions if you are interested in this.