Yes, Mayne Island falls on one of the main ferry routes between Victoria (Swartz Bay) and Vancouver (Tsawwassen) so several ferries stop in most days. It is also possible to arrive by short ferry journey or private boat from the nearby Gulf Islands (Galiano Island, Pender Island). Because the island is so small it can easily be explored in a single day, although if you have more time there is plenty to keep you busy for an entire weekend.