Have you considered taking the Crowsnest to Princeton and then north on Hwy 5A to Kamloops?
Choices are limited - esp. if you intend to stay on pavement - but Hwy 97 can be busy around Kelowna.

Machka is right - Hwy 5 is your only paved choice up to Valemount - and even through forest roads are few and far between.
There are local roads on the other side of the river from Hwy 5 - paved/unpaved??
I was on Hwy 5 so I cannot tell you. Also, they might not be through roads.
North of Clearwater, Hwy 5 was quite nice with only moderate traffic.

Looking at BC AADT date -
http://www.th.gov.bc.ca/trafficData/index.asp

A lot of Hwy 97 has traffic counts exceeding 10,000.
Busier parts of Hwy 5A have in the range of 6000 - rural stretches below 2000.
The northern section of Hwy 5 has in the range of 4000+.

All of those numbers are busier than I like.
But the lack of paved alternatives means that the few paved roads concentrate all traffic

BTW - Traffic Data collection appears to be politicized in BC. (Isn't everything?)
Higher numbers mean more road money - so these numbers could be inflated.