I'm not sure this is even remotely feasible. IIRC the Japanese used fleas as their vector. I'm not sure whether they'd bomb California with human fleas or rodent fleas, but neither sounds terribly promising as an approach. Does the West Coast even have significant migratory rodent populations? Sure, port rats, but you can't bomb urban areas with these, it'd be noticed immediately. Human fleas are going to be pretty pointless in the age of DDT.
I suspect that perversely, the best success would come from failure. If the attack was detected immediately and interpreted correctly, public health authorities up and down the coast would go absolutely ape. In wartime, they can wield powers to do very unpleasant things - slum clearances, condemning buildings, population transfers, mandatory delousing. The temptation to relocate a few unhygienic pigmented populations for postwar development of their land might become too great in the process, but even if not, you could see the stories spreading of how the police came to burn down uncle Rodriguez' shack, and when the neighbourhood fought back, the army came and machinegunned the damn greasers, served 'em right. So much for Double Victory. Then there would be navy units drawn away from other theatres to patrol the West Coast for more Japanese submarine carriers. Even if they don't score a few US subs by accident, they'll be pretty useless.
The actual plague outbreak would be a small problem by comparison. Modern health measures can contain bubonmic plague quite effectively if the resources are in place.