How are you planning on getting from Banff to Columbia Falls?

I'll recommend variations of the route I did. I decided to try some of the GDMBR though ended up more on the adjacent roads. The only spot I definitely needed to be on trail was 6.2 miles of Elk Pass which I mostly hiked with my bicycle. Otherwise I had choices of either road or trail to experiment. Near Banff I was on trail and the gravel roads would have been somewhat dusty. Near Fernie, I took the "old route" which was paved though there was a new off-road section that was described as rougher. South of Eureka I took the Whitefish Divide Road. Don't have to take the exact same choices I did but along this general route there is are a good set of alternating choices.