I spent three weeks in Canada in 2014. We were around the Jasper and Banff are for around half of that.
Rather than Banff directly, we stayed in nearby Canmore. There's loads of awesome hikes to do in the surrounding area. And if you go up to the Nordic Centre in the summer, you can hire bikes and go around all the cross-country skiing trails. I definitely recommend a hike up to the ink pots in the Banff National Park.
It's such a beautiful area and it's my favourite holiday I've had in my life so far. I would not hesitate at the opportunity to go back. You can read my trip report for a bit more information and pictures :).