There are 2 main areas for chartering in BC: the Gulf Islands between the mainland and Vancouver Island, and Desolation Sound, north of Vancouver. The most convenient charter base for the Gulf Islands is Sidney, just north of Victoria on Vancouver Island. Vancouver is also a major charter base, across Georgia Strait from the Gulf Islands, and a couple of days (at least) from Princess Louisa Inlet, up the Sunshine Coast. Ports in the islands are pretty close together. Sailing to Desolation or Princess Louisa from Sidney or Vancouver takes 2 or 3 days, so if you want to be IN Desolation Sound, it makes sense to charter out of Powell River or Comox.

http://salishseapilot.com/ is a pdf cruising guide to the San Juans and Gulf Islands.
The Waggoner Guide is useful for the whole BC coast and Puget Sound/San Juans.
http://www.boatersbluepages.com/ChartersAndBoatRentals is a directory of BC based charter and rental companies.

I have no experience with charter companies here, though I know Cooper is the biggest and has bases in Sidney, Vancouver and Powell River.

Expect to do a fair bit of motoring in July. The Gulf Islands are the most populated area, and lovely. Desolation is spectacular - fewer marinas, and anchoring often with stern ties as the water is deep. Princess Louisa is stunning.

It's a wonderful part of the world for sailing. Alertness to significant tides is important. Some passes can have currents between 10 and 15 kn. I suspect the charter companies do a good job of orienting people.