You must set your RV up at a designated campsite. If you pull into a rest stop or by a river or something, you will be told to move along and you might be fined.
Here is some information about Banff National Park (southern end of the Icefields)
http://www.pc.gc.ca/pn-np/ab/banff/index.aspx
And Jasper National Park (northern end of Icefields)
http://www.pc.gc.ca/eng/pn-np/ab/jasper/index.aspx
If you click on the Visitor Information, and then Where To Stay, you'll find information on where you can stay in the park:
http://www.pc.gc.ca/pn-np/ab/banff/visit/visit3.aspx
http://www.pc.gc.ca/pn-np/ab/banff/v...it9b.aspx#camp