I have been there a couple of times. At the park entrances you will be able to pick up free trail guides and maps.
Excellent water repellent maps can be had from gemtrek (either gemtrek.com or gemtrek.ca) direct or in some map/book stores. I can't recommend these highly enough. They are primarily topographical trail maps although they also have some driving maps.
Ditto on Jasper and Banff. You didn't say how long your trip will be but we spent 12 days in Banff/Jasper on each of our two trips and plan to go back several more times.
BTW, September is a good time, the bulk of the insane tourist traffic is gone, although the hiking trails, even the short ones, are usually deserted. Most tourists stay close to the buses. Bring a lot of sweaters and dress in layers. The last time we were there it snowed in Lake Louise in the 2nd week of Sept.
If you drive between Banff and Lake Louise take the scenic route choice, not the main highway. Visit Johnson Canyon.
Allow a day to drive from Banff to Jasper. You can drive the distance in 2.5 hours but that's missing the point. Too many photo ops to count.
Mt Edith Cavell can be a cold drive and hike, but worth it, just south of Jasper.
Check out "
http://www.parkscanada.gc.ca/" for up to the minute trail conditions. Check with local rangers before heading out on a hike.
If you don't mind stenuous walks, climb up Parker Ridge on the Icefields Parkway, about 8 km south of the Columbia Icefields Museum and rest stop. Go all the way to the back side of the ridge when you reach the top. Bring hats and gloves for that climb. About a 2 hour climb; only 45 minutes to go back down though.
When in Lake Louise hike to the Lake Agnes tea house. It took us 2.5 hours but we're out of shape. Again, about 45 minutes down.
That's all I can think of for now.
