I just came back from Kelowna!
I took the same route as you are planning, but I didn't get a chance to fish.
If you have a National Parks license, try Wapta lake. It's about 10 minutes before you hit Field in Yoho national park. Also in the park, try the Kicking Horse River.
http://www.pc.gc.ca/pn-np/bc/yoho/visit/faire-do/a.aspx
There are a few hike-in lakes along the same route.