Dec 8 (Reuters) - Canada’s main stock index opened lower on Tuesday, dragged by energy stocks, as surging coronavirus cases across United States and Europe spurred talks of tightening restrictions to curb the spread. * At 09:30 a.m. ET (1430 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 35.55 points, or 0.2%, at 17,546.8.