How about, instead of (or as a prelude to) splitting the state, we change the 55-electoral-vote winner-take-all system in CA and allow each Congressional district to be a mini-state with its own EV? The two Senate EV's could go to the overall winner of CA.
After all, the population of each district in CA is about the same as the population of Vermont, Alaska, or North Dakota, and CA is still growing.
Assemblyman Tony Strickland proposed this in 2000, although the Democrats obviously didn't like the proposal.
Another option is to reduce the power (and funding) of the state government and restore power (and taxes) to the local counties. Then there would be less need to break up CA.