Hoping to capitalize on the deregulated electricity market coming soon to California, Sunlaw Energy Corp. is proposing to build an 810-megawatt, natural-gas-fired power plant in Vernon that would start operation in 2002. The $450-million plant would generate about one-third as much energy as San Onofre Nuclear Generating Station and would sell its electricity into the statewide Power Exchange starting up next year. Sunlaw is an independent power producer that operates a 64-megawatt cogeneration facility in Vernon that sells energy to Southern California Edison. The company, based in Vernon, also makes air-pollution-control catalysts for industry. The new power plant would be financed by Sunlaw Cogeneration Partners, whose largest investor is John Hancock Life Insurance of Boston.