Nanaimo's an easy ferry ride from Vancouver, so even a day trip is possible. I also like Diver's Choice, although there are other options for charters in Nanaimo.
Victoria is also a ferry ride away, and Ogden Point Dive Shop runs charters out to Race Rocks, as well as the McKenzie and a few other great dive sites.
There used to be a dive shop in Vancouver (BC Diver Adventures) that ran a small boat out to some really nice dive sites around Bowyer Island. I think he sold the boat, but it's still in service for diving. You could check with the shop.
There's also some pretty nice shore diving up at WhyteCliffe Park, just south of the Horseshoe Bay ferry terminal in north Vancouver.
You've got lots of options ... and April's a great time to be up here diving ...
... Bob (Grateful Diver)