You could spend a couple weeks or more on Vancouver Island ... touring from south to north and back. Starting from the south ...
Victoria - dive the wrecks of the McKenzie and Church ... then the second day head out to Race Rocks. The former gives you two excellent wrecks prepared as reefs in easy, recreational depths. The latter is a life-filled wonder that offers a rich diversity of fish and inverterbrate life ... and if you're lucky you might get buzzed by some curious sea lions.
Nanaimo - more wrecks ... the Sasketchewan and Capt Breton. The former is sister ship to the McKenzie, but placed a bit deeper and in more nutrient-rich waters .. it's covered with life. The Breton is a larger ship, and slightly deeper still although its upper deck is in less than 100 feet, and top structure in as little as 70. Both of these vessels are covered in life. After exploring the wrecks, hit some excellent reef structure along Snake Island Wall and Jesse Island. And if tides permit, take a ride along the walls of Dodd's Narrows.
Campbell River/Quadra Island - walls, oh-my-god colors, and intense marine life. Be prepared for challenging conditions and sensory overload.
Port Hardy/Browning Pass - all roads north lead to here ... hop on a boat at Pt. Hardy, or stay at one of the two "resorts" out in the islands, and enjoy some of the best diving you'll find anywhere on the planet. I've heard it described as Quadra Island on steroids ... and that's an understatement. Life doesn't just cover the walls here ... life grows on top of the life. Due to its remote location, it's one of the few truly "unspoiled" dive destinations remaining on this planet ... and well worth the effort to get there. And topside views are nearly as worthwhile as the underwater ones, with rafts of otters, orcas, humpback whales, stellar sea lions, and pods of Pacific Whiteside dolphins commonly encountered.
Nootka Sound - head back to Campbell River and then turn west to cross the island to the inland tip of Nootka Sound. The tiny town of Tahsis offers just one dive operation, so you won't likely see another diver except those on your boat the entire time you're there. Truly wild northwest scenery, much like Port Hardy, but diving an inland fjord rather than open ocean offers different vistas and marine species. This is a great place to visit in the fall, when the salmon are running ... one of the highlights is snorkeling a local river with the spawning salmon. Just keep an eye out for bears ... they don't like the competition.
Barkley Sound - heading back south, turn across island toward Port Alberni ... or make your way around to Bamfield on the west side of the island. But my recommendation would be arranging at least a three-day stay at Rendezvous Lodge, situated on a shelf of rock in the middle of nowhere. The diving here is remote, spectacular, and completely different from anything you'll have seen up to this point. Probably one of the best chances anywhere on the island to encounter six-gill sharks. Once again, topside views are as absorbing and spectacular as the underwater views. Renate's Reef is a "must see" ... a pinnacle rising out of the depths to a depth of about 30 feet, completely covered in life and home to some of the largest ling cod I've ever encountered.
These are just the highlights ... there are numerous other diving places along the way that are also worthwhile as day trips or multi-day stopovers.
... Bob (Grateful Diver)