You bring up an interesting issue with equalization payments. California would be a "Have" province and hefty transfer payments would probably be expected.
But mostly, I'm just concerned that California would immediately become the dominant political entity in Confederation. Right now, the centre of the world is basically Toronto. Suddenly, the financial, technological, and industrial centre of Canada would all be in California. I can't see that going super well. People and businesses would migrate en masse. It could lead to an impoverishment of other Canadian provinces as the capital all moves to California.
Population, GDP, culture.. Canada would be eaten alive by California. They wouldn't change. We would.
Maybe. Not convinced it'd be best for Canada, though. I think California would be better as an independent country that we could then negotiate with on more or less equal footing.