Dec 17 (Reuters) - Canada’s main stock index extended gains for a third straight session on Thursday, as gold miner stocks gained, while hopes for fresh stimulus in United States further lifted sentiment. * The materials sector, which includes precious and base metals miners and fertilizer companies, added 2.7% as gold futures rose 1.2% to $1,878 an ounce. * The sector’s gains were led by the largest percentage gainers on the TSX, Seabridge Gold Inc and MAG Silver Corp, which jumped 5.2% and 4.5% respectively. * At 9:37 a.m. ET (14:37 GMT), the Toronto Stock Exchange’s S&P/TSX composite index was up 98.08 points, or 0.56%, at 17,665.5. * The optimism in the Canadian market followed the upbeat rally across global markets after U.S. congressional leaders sounded more positive about a $900 billion stimulus package. * Adding to the upbeat mood, the energy sector climbed 0.1% as U.S. crude prices rose 1.0% a barrel, while Brent crude added 0.7%. * On the TSX, 149 issues advanced, while 66 issues declined in a 2.26-to-1 ratio favoring gainers, with 16.15 million shares traded. * Aurinia Pharmaceuticals Inc fell 9.7%, the most on the TSX, after the biotech firm announced a licensing agreement with Otsuka Pharmaceutical Co Ltd. * The second biggest decliner was pot producer Aphria Inc , down 5.8%, after brokerage Stifel downgraded it to “hold” from “buy”. * The most heavily traded shares by volume were BCE Inc , Canadian Imperial Bank of Commerce, and Air Canada. * The TSX posted six new 52-week highs and no new low. * Across Canadian issues, there were 74 new 52-week highs and four new lows, with total volume of 32.55 million shares. (Reporting by Amal S in Bengaluru; Editing by Vinay Dwivedi)