1. At the top of the island is the famous Cape Scott. While people think of this as a serious hiker's park (for the well-known Cape Scott Trail) it has some easily accessible day-use areas, including the beautiful sandy San Josef Bay. Wilderness camping is allowed in this park, but there are no services. Just outside the San Josef entrance there is a private campground with cleared sites and picnic tables.
4. Marble River, at the edge of Quatsino Sound, is an easy river park to access (via logging roads) and there is a forestry campsite just outside the park boundary. Marble River offers hiking and biking trails as well as good angling.
A number of the parks on the north island are much more difficult to access and in fact some are almost inaccessible. Much of the access into the northern portion of the island is dependent on logging roads, and once a road is deactivated it is no longer serviced and can quickly become impassible. This has happened with the Artlish Caves Provincial Park, where there is now a hike in to the park as the logging road access was deactivated several years ago. These parks have been established to protect sensitive habitats and ecosystems, so creating access is not a priority for the parks program.
You can discover all the provincial parks (and ecological preserve areas) through the BC Parks website. A good place to start is the geographical locator page, which lets you zoom into the region you want to explore.
Vancouver Island north of Campbell River is a massive space that may seem empty as the communities are small and spread out, but for the intrepid explorer there are some beautiful areas to discover. Doing a circuit of Provincial Parks is just one way to get out there.