The Banff Jasper Highway in Alberta - hands down the most beautiful highway in the Country. Actually any of the roads or highways in the Rockies is fabulous. What we referred to loosely as the Rockies is actually 4 mountain ranges - the Rocky Mountains and the Purcells in the east, and the Selkirks and Monashees in the west. They start, going from east to west , in Alberta with the larger portion of them being in B.C. from the Alberta/B.C. border all the way to Vancouver and the Pacific.
http://www.travel.bc.ca/regions/
The Cabot Trail at the other side of the country, also very beautiful but very different. The Cabot Trail is located on Cape Breton Island in Nova Scotia. This is also mountainous but a very different type of Mountain from those on the west coast. Like the west coast, they do go right to the ocean's edge - the Atlantic. Rugged and postcard perfect. If you like the ocean, you will love Nova Scotia. The Cabot Trail is one of the more famous but there are others so here's a url where you can read up about the others.
http://novascotia.com/en/home/default.aspx
Those two would be what I would pick as the two best but the entire country is worth a look. Gee! I spent 40 years driving back and forth from one ocean to another and loved every minute of every trip. Each province has things that are outstanding and unique to them. The Prairies are seldom gushed over like the others - they are flat. But 'you ain't seen nothin' till you have driven across the prairies at harvest time or fly over them when the flax and the canola are in bloom. It looks like a yellow and blue and gold patchwork quilt. An amazing site.
Quebec and Ontario are not just beautiful to see, they are full of Canada's early history. If you want rugged - definitely go to Newfoundland. PEI and New Brunswick - also maritimes, each with it's own flavour that is different from all the rest.
If you are planning a trip it might help to know that Canada is a teeny bit bigger than most places - 6,416 km - 2 878 km of land + 3 538 km of water from Atlantic to Pacific. These are the Canada/US Border figures.
http://www.internationalboundarycommission.org/boundaryfacts.html
Hope this helps