If nobody responds regarding your specific trip, I'd be happy to answer any questions you might have on the route from Banff to Whitefish. I did the entire GDMBR in 2010.
You'll be pleased to know that I, at least, thought one of the best parts of the route was from Banff to Elkford. The route starts at the back of the Banff Hotel through a well groomed dirt bike path with gentle ups and downs to a gravel road that leads you to Spray Lakes. You'll enjoy lots of wildlife and panaoramic vistas. Plenty of clean-looking water that one might consider drinking without filtering (if treated). The weather will be warm at the relatively low altitude, so a light sleeping bag is OK. Always be prepared for rain, however.
After Spray Lakes the trail becomes a bit rougher, but shouldn't even be considered single-track - something you won't experience since you're not going through the Flathead Wilderness. Great scenery and the chance of a grizzly encounter - possible all the way to Elkford and from the turnoff south of Eureka to north of Whitefish. Get your bear spray in Banff - much cheaper than in the US and legal to use there. You probably won't use it, but for me it can me some comfort when things went bump in the night. Good on dogs too, for when you get home.
After Boulton Creek you'll have some short sections of hike-a-bike to Elk Pass, then pretty much downhill on packed gravel to Elkford where you can resupply at a proper grocery store.
After Elkford, gravel, then hardtop to Fernie. Not really mountain biking. Also asphalt all the way to Graves Creek, after which you have a gravel road that gets rough over the pass, then well-graded to Polebridge and on to Whitefish.
If you are a more advanced mountain biker and haven't been intimidated to Elkford, you might want to consider teaming up with a like-minded companion (or two, three) and eschew the asphalt from Fernie and instead do the Flathead Wilderness section that will be on your new ACA GDMBR maps. You can rejoin the rest of the group at Eureka or just continue down the valley to Polebridge. If you forget about the scheduled rest day in Fernie, you will have ample time. Don't decide now, think about its doability when you arrive in Fernie. Lots of conversation about the Flathead at
http://www.bikepacking.net/forum/index.php?PHPSESSID=b67d558604bc312b6bac3e525aa0a709;wwwIf you still have time and energy, it would be well worth peeling away from the group at Polebridge and exploring Glacier National Park. Or, just go to GNP from Whitefish at the conclusion of your tour. Avoid the KOA in Whitefish. It's waaaay south of town and they tried to charge me $40 for a tent site.
If you have any questions, just ask!
