TORONTO, May 12 (Reuters) - Canada's main stock index opened higher on Monday as gains in the prices of commodities such as gold, copper and oil helped drive up shares of natural resource companies. The Toronto Stock Exchange's S&P/TSX composite index was up 53.07 points, or 0.37 percent, at 14,587.13 shortly after the open. (Reporting by John Tilak; Editing by James Dalgleish)