Every state gets one EV for each US House Rep and one for each Senator. So the smallest states have 3 EVs. (DC has 3 EVs too, by Constitutional Amendment).
Congressional districts roughly contain 700,000 citizens.
So, after partition the two states would split up the reps, with each getting however many their new population required, but the total staying the same. (There might be a fight about that last one that needed to be split in 1/2, but regular reapportionment would adjust things going forward anyway).
The news State would get two Senators, the old State would get two Senators. As a result the total EV's for the two resulting states would go up by two.
The exact breakout would depend on population. Given that the big population centers are all in the "Old California" they would probably end with the lions share.
Here is the map of the existing districts, which sort of gives you and idea.
