OP, to your question, the following are both great sites, although neither will show every campsite. Another option is to use Google Earth. Just zoom in to the area you want and type "camping" in the search box. As mentioned above, every province has a tourism website where you will find listings for campsites.
After travelling for the last 5 months in both Canada and the US, I can say that I have never had to use more than my 50 feet of power chord.
Generally, campsites are the same no matter where you go in either Canada or the US. However, in provincial campgrounds, power and sewer hookups are usually not provided. If you like to camp in natural settings with much more privacy, these will not disappoint. I hate camping in a sardine can between painted lines on a paved parking lot.
Time of year will dictate whether or not you will need a reservation. Best to check ahead if you can.
Hope this helps.
http://www.camping-canada.com/index.asp
http://www.allstays.com
