To get to the island my suggestion is the Gulf Isalnd fery from Tsawwassen (Pron. Twassen). It is a longer trip but much more scenic than Duke Point or the trip to Departure Bay.
As some have already mentioned check out Butchart Gardens in Victoria. Also look into the wax museum in Victoria, and just around the corner is Undersea Gardens.
Farther north on the island look at the Cowichan forestry museum, if you like golfing look at Crown Isle golf course in Courtney.
Make a stop at the salmon fishing capital o fthe world. Campbell River, is also next to Elk Falls Provincial parks. There are t5rees in te hpark almost as large as the redwoods in California.