I would say no, and I would expect any sensible country to bar this within its borders. To the extent that a state should have a nonviolent means of secession, this above all should not be subject to foreign interference.

You can find a more detailed view of my opinion on specific independence movements elsewhere in this thread.

Regarding California or indeed any other state breaking away from the US, it's none of our business. And, before you ask, in the highly unlikely event that they wished to join Canada, I would expect them to gain independence and then, separately, start any process of joining another country.