(Adds details; updates prices) Dec 29 (Reuters) - Canada’s main stock index reversed initial gains to fall on Tuesday, dragged by materials stocks, although the approval of a $2.3 trillion coronavirus aid package in the United States kept sentiment in check. * The materials sector, which includes precious and base metals miners and fertilizer companies, lost 0.7%. * Pot producer Aphria Inc fell 4.2%, the most on the TSX, while the second biggest decliner was cancer drug developer Trillium Therapeutics Inc, down 4%. * At 09:38 a.m. ET (1438 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was down 22.95 points, or 0.13%, at 17,600.93. * The Democratic-led U.S. House of Representatives on Monday had voted to meet President Donald Trump’s demand for $2,000 coronavirus aid checks for Americans shifts. * The energy sector climbed 0.3% as both U.S. crude and Brent crude futures added 1.3% amid U.S. moving towards expanding its coronavirus aid checks to $2000 from $600. * On the TSX, 122 issues were higher, while 95 issues declined for a 1.28-to-1 ratio favouring gainers, with 18.01 million shares traded. * The largest percentage gainers on the TSX were miner MAG Silver Corp, which jumped 3%, and power producer TransAlta Renewables Inc, which rose 2.6%. * The most heavily traded shares by volume were Power Corporation of Canada, TC Energy Corp and Zenabis Global Inc. * The TSX posted seven new 52-week highs and no new low. * Across all Canadian issues there were 109 new 52-week highs and seven new lows, with total volume of 48.60 million shares. (Reporting by Amal S in Bengaluru; Editing by Amy Caren Daniel)