Crossing the border just to get into Vancouver, towing what you have, is not a great idea. There are few CGs in the metro Vancouver area and all are packed in the summer. I would only do this if you intended to head up the Fraser Valley to Chilliwack or further to around Hope. There are a number of good CGs around Chilliwack.
I would wait until another time when your specific destination is BC. In that case I would go to the Olympic Peninsula and take the ferry from Port Angeles to Victoria on Vancouver Island. Then head up the Island to Comox, take the ferry over to Powell River on the Sunshine Coast and make your way down to Horseshoe Bay in West Vancouver. From there you could head into Vancouver, up the Fraser Vally, go back to Vancouver Island or head into the Interior via Whistler to Pemberton. This route has beautiful sites and scenery and takes you around the protected waters of Georgia Straight. The fares on BC Ferries are quite high though, esp. if towing an RV.
