Been across most of the country, and love what I've seen. From the Eastern tip of Newfoundland (don't forget Gros Morne - unreal - on the must go back to list...
http://www.google.com/search?q=gros+...w=1381&bih=735), to NS, NB and PEI... Good places. Quebec I really want to see Quebec City, I've heard it's spectacular...
Ontario... well, the Rideau Canal system, the shield country, home of Big Joe Mufferaw, the great lakes (helps I get off the beaten tracks)... Can't say I've seen much of Manitoba or Saskatchewan, but Alberta and BC I love.
If I were a young and single man though, I'd probably be up north of Lliard and into the Territories or Northern BC (Atilin maybe?). I did a canoe trip from Marsh Lake (south of Whitehorse) to Circle City, Alaska. I really want to take Dad on the stretch from Whitehorse to Dawson. Spectacular...