Travelling from Alberta through BC/Advice needed

The steepest grade will be on the Tofino leg. Port Alberni to Uclelit (sp?) has a steep downgrade - curvy as well.

Next major downgrade is Hwy 5 Merritt to Hope. After the summit there is a long grade. But it is divided highway. Hwy 1 along the Frasier River does not have grades like this, but it is longer and curvier. And 2 lane south of Cache Creek.

Further east is Rogers Pass on Hwy 1. There's a long steady grade from the Pass to Revelstoke. But there are good stops along the way where you can rest and hike a bit. And earlier on 1, there is Kickhorse Pass. The climb from Lake Louise to the pass is negligible, but the drop through Yoho Nat Park is long and steady. But you can stop to look at the railway loops, and several side trips to sights in the park. This is the main highway across the country, divided where space allows.

If instead you take the Parkway north to Jasper, there is a long gradual drop from the Athabascan glacier to Jasper. Passes and grades west from Jasper to Hwy 5, and south to Kamloops are minor. Traffic is also lighter than on Hwy 1 through Yoho and Rogers.

The weather in the high mountain passes can change rapidly at this time of year, the Banff town site has already seen a bit of snow. There is a long steep grade south of the Athabasca glacier so use your brakes sparingly. Slow down at the top and use the tow/haul mode to control your speed, snub the brakes occasionally to keep things out of the white knuckle range but don't ride them. Long steep grades are a fact of life here so drive accordingly. Fuel up in Jasper, the next opportunity is Field unless you are prepared to get gouged at Saskatchewan River Crossing.
Many campgrounds are closed for the year, you cannot stop in undesignated areas in the parks so govern your time accordingly. Golden has a nice one by the river if it is still open. Best to call ahead.

Already consistently below 0 celsius at Jasper. We were up there 2 weeks ago, encountered some freezing rain on the Icefields Parkway, which was "interesting".

On the other hand, I drove the Parkway one year in February at -40 -- it was bloomin' cold,but gloriously scenic!

The flattest route, although parts of it can be quite boring, is to drive Hwy 5 from Jasper to Kamloops and then Hwy 1 to Vancouver. Use your transmission to slow you down on the hills rather than your brakes, which should be used sparingly to avoid overheating and fading.
You do need winter tires in BC, but the minimum requirement is for tires to be marked M+S, which most? truck tires already are? You do however, need full snow tires, marked with the 'Mountain & Snowflake' on the Icefields Parkway between Lake Louise and Jasper.

Keep in mind that in B.C. they require snow tires or chains from October 1 to I think April 1. I only really paid attention to the Oct date because we were on our way home and would be out of the mountains by then. Pump your brakes so they don't overheat. I forgot and had to have the rotors turned while on our trip.
Check ahead for campsites as some were closing when we were there mid to late September.
Safe travels
Brian

From Kamloops, go to Cache Creek then down through the Fraser Canyon. It's very scenic and while it's up and down a bit, not nearly as high as other routes. There is a nice campground in the middle of the canyon called Skihist that is a BC park with a dumping station too.

From there, drive to Horseshoe Bay and take the ferry. Be prepared for a ticker shock, it's about $290 each way.

It's still a long ways to Tofino, so plan a night camping, perhaps at Qualicum River Falls. It's just west of Coombs and along your route to Tofino. Some nice easy hiking there.