(Updates prices, adds comments) Sept 17 (Reuters) - Canada’s main stock index hit a three-week low on Friday, weighed by energy and mining stocks, as investors were cautious ahead of next week’s federal election. All eyes are on the outcome of next week’s election called by Canadian Prime Minister Justin Trudeau, seeking a parliamentary majority after two years of a minority government. “It looks like the market is assuming that one of the two middle-of-the-road parties is going to win a minority, which limits their ability to do things because they still have to work with the other party,” said Colin Cieszynski, chief market strategist at SIA Wealth Management. “So unless we have a significant deviation from that, the overall impact on the index is likely to be fairly limited.” The Toronto Stock Exchange’s S&P/TSX composite index dropped 0.36% to 20,528.24 by 9:45 a.m. ET, and was set to post its second consecutive week of losses. “For Canada to see some weakness in September is not unusual, given seasonal factors in global equity market trends right now,” Cieszynski added. Persisting fears of slowdown in economic recovery amid rising global COVID-19 cases has dented investors’ appetite for global equities in September after seven straight months of gains. Among equities, the energy sector dropped 1.5% as crude prices fell, while the materials sector fell 1.1% after posting its worst session in two months on Thursday. HIGHLIGHTS * Canadian National Railway Co gained 2.1% after the railroad operator said it would resume a previously approved share buyback, days after walking away from its $29.6-billion deal for U.S. railroad operator Kansas City Southern. * Miners Labrador Iron Ore Royalty Corp and Teck Resources Ltd were the biggest decliners on the index, down 3.9% and 3.8%, respectively. * The TSX posted six new 52-week highs and three new lows. * Across all Canadian issues there were 13 new 52-week highs and 12 new lows, with total volume of 135.04 million shares. (Reporting by Amal S in Bengaluru; Editing by Amy Caren Daniel)