I suspect Sanchez will win. She will probably get the Latino vote which is crucial in California. She will probably get some Republican votes while Harris most likely won't get any. And she's also from S. California while Harris is from N California and S California is more populous.
Firstly, Sanchez is very gaffe prone and has said a lot more thing against the GOP. Harris is a lot more affable. It's the difference between some Tea Party guy and Chuck Grassley.
Secondly, the Bay Area has better turnout levels than LA.
Thirdly, the black and Asian votes themselves are hardly insignificant, and Harris will easily lock both of those up along with a good chunk of the white liberal vote based on recognition alone.
Finally, Harris has disproportionate funding on her side.
And as long as criminal justice is a huge concern nationwide and things swing as they do, Harris is going to have a serious edge and could well cut into the Latino/a vote on that alone.
And Sanchez is going to have to overcome all those factors to win...could happen, but very much a longshot.