The EU would be better off promoting separatism for the redneck states rather than specifically supporting California. Direct trade with California is tough, but if the southern states were to fall off, the east coast of the USA would still provide a decent area to trade with.
I always find it so interesting how little the topic of Californian independence comes up online. You would think there would at least be a decent amount of organic content around that, never mind external interference.
Separatism is born of a sense of ethnoracial exceptionalism:
1) we're a genealogically different ethnic group from the rest of the country
2) we're better than the major ethnic group of the rest of the country
Both bits are absolutely essential. I can't recall a single instance of a separatist movement based on purely political differences gaining serious ground, Alberta included.
Why just ethnic? It can also be religious, ideological, or based on some economic interest. The US revolution was a mix of tax revolt and ideology. The British were the same ethnic group as most of the leaders of the revolution.
It would be kind of a stretch to argue this as the reasons for separation of the US from the UK - I can see some of it, but I think the argument is a stretch.