Will Alex Padilla win? He seems very popular in California. I can't imagine a serious Democrat challenging a former CASOS who won by a wider margin than Gavin Newsom.
His pro-M4A/GND statements will probably stave off challenges on the left flank, but London Breed said his appointment was a blow to the African-American community and could challenge him from the right. I doubt she has the profile to win, but like Newsom and most other major officeholders in California (but not Padilla), she is from the San Francisco set and could build a base out of there if she could do it anywhere. That's a double-edged sword, though; emphasising that part of her background could turn off potential Republican supporters by reminding them of their history with SF Democrats.
Padilla supports court packing and abolishing the filibuster. I'm not sure if anyone would seriously challenge Padilla from the left.