Jeff, the South Boundary Trail between Brazeau Lake and Rocky Pass actually gets less use than the North Boundary, so that is another option. You may see others at Maligne Pass as it is not far and beautiful. It is the area north of the pass (which is a willow hell and not interesting) that is all but abandoned. If you want total solitude in Jasper's alpine, you can hike into Rocky Pass to Cairn Pass and back. The Cairn Pass area is stunning, with lots of scrambles.
If you look at topo maps, the Nat Geographic 1:100,000 maps are the best for an overview, and they show all the official trails and campgrounds. If you need 1:50K NTS topos, the versions that Gotrekkers.com sells have all the official trails and campgrounds for Jasper NP overlaid on them as well, so they are a good resource if you plan to go to the remoter parts of the park.
And you'll be able to book all of Jasper's official backcountry campsites online as of the 28th, at www.pc.gc.ca/bookjasperbackcountry. You will also be able to see how full each campsite is as the season progresses, so it will give you an idea of how busy a trail is. There will be detailed trail guides for all of the official trails online at www.pc.ca.gc.ca/jasperbackcountry in the next month or so.