Did Spanish explorers realize its island nature?
Well, Juan de Fuca (in the 16th century) definitely didn't get far enough to realize it was an island, although Malaspina (in the 18th century) may have realized that it was...
Possible alternate names: (in relative order of likelihood)
- Juan de Fuca Island (after the explorer who discovered the Juan de Fuca Strait)
- Malaspina Island (after a later Spanish explorer who explored the area - he was a contemporary of George Vancouver)
- Anian Island (the 'Strait of Anian' was a legendary Northwest Passage which separated the 'Island of California' from the rest of North America - Juan de Fuca originally thought he had discovered the Strait of Anian when he first entered the OTL Strait of Juan de Fuca, and the name 'Strait of Anian' could have stuck, and then the island could have been named after the Strait)
- Nootka Island (Nootka Sound was the most important 18th and early 19th century anchorage on *Vancouver Island, and thus the island could have been named after it)
- Galiano Island (after the Spanish explorer Galiano who was the first to circumnavigate *Vancouver Island)
- Quadra Island (after the leader of the Spanish settlement at Nootka Sound)
- Salish Island (after the Salish people who inhabited the area - this would likely be a 20th/21st-century re-naming like the OTL *Salish Sea, or the pre-colonial name Haida Gwaii being used for what used to be called the Queen Charlotte Islands)
- King George Island (after King George III who was King of the UK at the time - goes well with the nearby 'Queen Charlotte Islands')
Just curious, why are you interested in alternate names? Are you working on a TL involving the area? If you need any geographical info or info about the Coast Salish peoples, I have first-hand knowledge of both, feel free to PM me.