July 8 (Reuters) - Canada’s main stock index opened lower on Thursday, weighed by a drop in energy stocks as crude prices extended losses on supply uncertainty. * At 9:33 a.m. ET (13:33 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 190.46 points, or 0.94%, at 20,100.14. Reporting by Amal S in Bengaluru Our Standards: The Thomson Reuters Trust Principles.