June 14 (Reuters) - Canada’s main stock index opened lower on Monday, as weakness in mining stocks and dismal domestic manufacturing data overshadowed gains in energy stocks. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 19.71 points, or 0.1%, at 20,118.64. (Reporting by Amal S in Bengaluru; Editing by Rashmi Aich) Our Standards: The Thomson Reuters Trust Principles.