Aug 20 (Reuters) - Canada’s main stock index was flat on Friday, but was still on course to snap a four-week winning streak as a slump in oil prices dented demand for heavyweight energy stocks. At 9:31 a.m. ET (1331 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up just 6.27 points, or 0.03%, at 20,221.63, while the energy sector dropped 0.7%. (Reporting by Sagarika Jaisinghani in Bengaluru; Editing by Maju Samuel) Our Standards: The Thomson Reuters Trust Principles.