Many potential suggestions. Are you looking for only outdoor places? or also city landmarks and events. Also, what part of Canada?
You may consider these lists
http://www.destinationcanada.info/ca...tractions.html
based on estimated attendance
http://www.ratestogo.com/blog/touris...ons-in-canada/
as voted by readers of Sun Media
http://www.torontosun.com/2012/11/14...ions-in-canada
the 16 + 8 (submitted) UNESCO World Heritage sites
http://whc.unesco.org/en/statesparties/ca