British Columbia

Three weeks is ample time to do a circle tour that would include the Alaska Highway in British Columbia's north. This would include a quick dip into Yukon too, near Watson Lake.

The Cassiar Highway on the northwestern side of B.C. is one of the best routes for seeing bears and glaciers.

The Alaska Highway between Watson Lake and Fort Nelson is where the caribou, bison and bears hang out in late August or early September. As well, Liard Hot Springs provincial park is a great spot to spend a couple of nights soaking in the pool and relaxing.

The Cassiar and Alaska Highways have terrific provincial campgrounds. The Cassiar has three by lakes (Meziadin, Kinaskan and Boya) and the Alaska Highway has Liard Hot Springs and historical Kiskatinaw, as well as two campgrounds lakeside at Muncho Lake and another lovely one at Summit Lake. Watson Lake also has a gov't campground that is very nice BUT we usually opt for the commercial campground here to clean up and stock up at the nearby grocery store.

The Okanagan can easily be included northbound or southbound, via Hwy 97.

Having said all that, I must admit to also greatly enjoying the Kootenays in southeastern B.C. Very scenic. Relaxed. Good campgrounds. Soothing hot springs.

I second the okanagan valley. Beautiful. We stayed at wrights beach cg which was right on a lake in Pentitcon and also stayed on a lake in Vernon. Visited wells gray provincial park in Clearwater which was gorgeous.
Have fun !

I would highly recommend the Okanagan Valley (south-central BC) as part of your tour, especially if you are a wine lover. It is an area of long, narrow lakes in a glaciated valley, with hillsides terraced with vineyards, beautiful flowers and fruit trees everywhere, and wineries with great food as well as good wine--makes me want to be back there just thinking about it. And you will be there at the perfect time to stop at roadside stands selling fruit.

There are some nice provincial park campgrounds in the Kelowna area, although they are often very full during summer. Early autumn might be less crowded.

Google these areas and have a look, the West Kootenays is about an 8 to 10 hr drive from Vancouver ( Lower Mainland) in an RV without doing much but driving and refueling. This is not to say you wouldn’t take a few days camping on your way in and out of the Kootenays. So google these places:
Nelson BC, Kootenay Lake, Kootenay Lake Ferry, Kaslo. Paddle wheeler Moyie, Ainsworth Hot Springs, Halsyon Hot Springs, Nukusp Hot Springs, Idaho Peak BC, New Denver BC, New Denver Centennial Park Campground, Silverton BC, McDonald Creek provincial Campground, Summit Lake Provincial Campground, Three Islands Resort ( campground) Syringa Creek Provincial Campground Sandon BC. Nukusp BC, Valhalla Provincial Park, Slocan River , Cody Caves.
All the campgrounds that I listed are on Lakes
Soup

Coming this far, you should try to visit the Icefields Highway between Jasper and Banff/Lake Louise area.
In Victoria, Vancouver Island, visit Butchard Gardens, beautiful gardens and should be bloom in your time frame.
Capilano Suspension Bridge is a good sight along with short walk through the large timber.
Hell's Gate is a sight. It will not have large amounts of water during your time frame. It is a wonder during high run offs.
Stanley Park in Vancouver.