Aug 9 (Reuters) - Canada’s main stock index fell on Monday, with the heavyweight energy sector leading losses as rising COVID-19 cases brewed concerns over crude demand and pushed oil prices 4% lower. * At 9:30 a.m. ET (13:30 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 56.67 points, or 0.28%, at 20,418.75. (Reporting by Ambar Warrick; Editing by Subhranshu Sahu) Our Standards: The Thomson Reuters Trust Principles.