Where to start ... Vancouver Island is HUGE ... it takes about six hours to drive it south to north. Cutting across from the east coast at Parksville (about a third of the way up the island) and going across to the west coast at Tofino can take you another three and a half hours. There's good to excellent to downright mind-boggling diving all over the island.
Starting in the south ... Victoria is the biggest city on the island. There's some good shore dives, some artificial reef wrecks that are accessible by boat, a couple real wrecks, a HUGE breakwater that you can dive from shore, and an outstanding reef called Race Rocks. Hotels and restaurants ini the Victoria/Sidney area (Sidney's where the ferry comes in just up the coast) range from world-class to economy-class ... and there's lots of them. Ogdon Point Dive Centre is located on the breakwater, and offers full service as well as regular week-end charters to both the wrecks and to Race Rocks. I highly recommend them.
Nanaimo is probably the most well-known and easily accessible dive destination. Popular dive sites include the two ships located just off of Snake Island (Cape Breton and Sasketchewan). A third, smaller wreck (Rivtow Lion) is located just outside the harbor. Snake Island Wall is an outstanding deep dive. Jesse Island offers some real interesting topography, with swim-throughs and giant dendronotid nudibranchs in abundance. Clarke Rocks is only interesting if you've never seen wolf eels. Dodd's Narrows is probably the best dive out there, if you are lucky enough to be there at a time when the tide allow you to dive it. All of those are boat dives ... I highly recommend Diver's Choice charters. As for places to stay, my choice is the Buccaneer, which is right by the marina. It caters to divers. It's also right across from one of my favorite pubs ... Muddy Waters.
Couple hours north of there is Hornby Island. It's mostly known for sea lion and six-gill shark dives. Rob and Amanda run a diver's resort out on the island that is a fantastic place to stay and an interesting place to dive.
An hour or so north of there is Campbell River ... and a short ferry ride brings you across Discovery Passage to Quadra Island. Diving there is mostly walls, although there is another artificial reef located in Discovery Passage (Columbia) that is a real interesting dive. But the walls are amazingly loaded with life. These are mostly drift dives, as the current rips through this area ... which is where all the life comes from. There's two diving operations on the island. I'm not particularly fond of either one of them, frankly ... but it's what you get when you dive there ... and the diving's way worthwhile.
Couple hours north of there and you're finally reaching the far end of nowhere ... Port Hardy ... the apex cold water diving in all of Canada, if not the world. About an hour by boat from Port Hardy will bring you into Browning Pass ... at the south end of the Queen Charlotte Islands. The walls there are OH-MY-GOD amazing ... between the layers of life and the chronically good vis there's simply nothing on the island like it. It's a long ways away, it's expensive, and it's soooo worth it. The two "resorts" out there are God's Pocket and Browning Pass Hideaway. I've only stayed at the Hideaway ... and a few weeks back I posted a trip report right in this forum about my latest stay there.
Moving down the west coast, you've got Nootka Sound ... and Tahsis Charters. I haven't been there, but my friends who have rave about the place. It's one of the few places on the island where you can find red gorgonian sea fans.
A bit further down the coast is Tofino. I've been there, but not diving. Topside is drop-dead beautiful, and if you're going in summer, the campgrounds out there are wonderful places to stay. I've been told by a friend who took his boat out there that there's a dive shop in town, and that dive charters are available ... but can't verify that. He did say there's walls out there that rival Browning Pass.
Further south is Barkley Sound, and Rendezvous Lodge. You get to this place by driving to Port Alberni, then the lodge boat comes and picks you up ... it's a couple hours down through the Sound to the lodge, which is perched on a bit of rock on the side of a cliff. Diving there is mostly pinnacles, with some walls and one outstanding (real) wreck called the Vanlene. If you're going that far, plan to stay a few days.
You could spend an entire summer touring Vancouver Island ... just visiting the places I mentioned. All of them are worthwhile, some are simply outstanding, and the variety of diving from one place to the other is amazing considering you're doing it all from one (pretty dang big) island.
Pick your poison ... do some research ... ask more detailed questions ... or just plan to stay a coupla months and do 'em all. I gotta envy the folks who live out there ...
... Bob (Grateful Diver)