Oct 27 (Reuters) - Canada’s main stock index opened lower on Wednesday, dragged by energy shares on weaker oil prices, while investors awaited the Bank of Canada’s policy announcement due later in the day. At 9:31 a.m. ET (13:31 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 32.58 points, or 0.15%, at 21,140.87. Reporting by Amal S in Bengaluru; Editing by Ramakrishnan M.