SAN FRANCISCO (AP) - A trade tribunal has rejected a Canadian company's challenge to California's ban on the gasoline additive MTBE under the North American Free Trade Agreement. Methanex Corp., which produces an MTBE component called methanol, had filed a $970 million claim against the United States under NAFTA six years ago. The Vancouver-based firm claimed the state ban was aimed at removing foreign competition for American makers of ethanol, a potential substitute for MTBE, or methyl tertiary-butyl ether. The U.S. State Department has not officially announced the ruling and declined to comment on the case, said spokesman Steven Pike....