I spent most of my adult life on Vancouver Island and there is a wide variety of things to do. One of our favourites was to live on Mystic Beach for a few weeks nearly every summer. Not possible now that so many people have found it, but then it was fantastic! It's still worth the hike down and back up.
Chemainus is worth a couple of hours, too - the murals are world-famous, there are antique and other shops for browsing or buying, a great ice-cream place, and lots more.
Long Beach is wonderful, with the towns of Ucluelet and Tofino bracketing it. I hear the Inn there is great, but that's more recent than my visits.
There's also the little Gulf Islands - perfect for biking around, but if you plan to camp, find out which ones have sites - not all allow camping. Saltspring Island is a hotbed of art and craft. Tim Hume is world-renowned for his homing pigeons and his artwork. One of his carvings is in the collection of Queen Elizabeth II and the Duke of Edinburgh. A Canadian Navy ship took a collection of his work to Japan for Expo.
There's a funky campsite on Hornby Island, a co-op where each site has been built by the owning family and is unique. They used driftwood and rocks from the beach. The cabins are basic - wood bunks - you need to bring a sleeping bag and airmattress (or did when I stayed there). Google "Heron Rocks, Hornby Island" and you'll see pics and more.
Craigdarroch Castle is fascinating if you like history and incredible woodwork. It was built by an early coal baron for his wife. He died before it was finished, but she came out from Scotland with their 5 (?) daughters and raised them there. It's worth at least 4 hours. There's a tearoom, too.
The Museum and Art Gallery (and all the little galleries) are great, too. The Museum has a historic town with a working movie theatre - they show old Chaplin and Laurel & Hardy films - my boys loved it, and we stopped in at least once a week for years.
Butchart Gardens are unsurpassed, too, and on Saturday nights (check in case this has changed) in the summer, they have fireworks at dusk and the fountains spray in time to the blasts.
There is so much more, too. Check out the Blue Carrot Cafe and owner Cecil Oakes' artwork. You can see some of his pieces on his website. His murals and some of his paintings are created in one-colour layers, in a style pioneered by Maxfield Parrish.
High tea at the Empress is another cool thing to do. I hear the renovation was stunning, but haven't been back with time to go see it. And afterward, walking along the Inner Harbour is a perfect pastime.
The Tally-Ho horse-drawn wagons are fun, but I like the carriages even more - they are more personal. Black Beauty is a great company. I used to work for a competitor, but that company went out of business some time ago.
Well, that should get you started . . . Have fun!