July 27 (Reuters) - Canada’s main stock index opened lower on Tuesday, as energy stocks were dragged down by weakness in crude prices, while investors remained on the sideline ahead of the two-day U.S. Federal Reserve meeting. * At 9:31 a.m. ET (13:31 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 67.27 points, or 0.33%, at 20,097.69. (Reporting by Amal S in Bengaluru; Editing by Shounak Dasgupta) Our Standards: The Thomson Reuters Trust Principles.