I've lived just about everywhere on Vancouver Island at one point and now I'm in Victoria. Tofino, like everyone else suggested, is a must. The rest depends on what you're looking for; Victoria is great and very well presented. I would probably say you could do Victoria in a day or two though. There's lots of shops and attractions around town to see. For nature Botanical Beach sounds great. Also Bamfield is a huge marine biology attraction. Do a google search and check it out. This place is considered to be one of the nicest attractions in the world if you can get there:
http://www.bigpacific.com/whattodo/princess.html