Vancouver Island has a tourism website which would be a good place to start @
http://vancouverisland.travel/pub/islandtime/
The whole island though has several distinct zones, you could never do it all in a few weeks. Personally, I quite like the Parksville/Qualicum areas and then Pacific Rim Nat'l Park (Tofino, Ucluelet). Or Victoria would also be good. Each of those areas you should spend at least a week.