Canada's main stock index fell on Friday, weighed by losses among natural resource stocks as commodity prices pulled back, muting a strong weekly gain for the index.

The Toronto Stock Exchange's S&P/TSX composite index ended down 63.5 points, or 0.39 per cent, at 16,349.44. It nevertheless notched a 0.9 per cent gain over the course of the holiday-shortened week.

Half the index's 10 main groups finished in negative territory, with decliners outnumbering advancers by almost 2-to-1 overall.

The energy group fell 2.3 per cent, as oil prices retreated from highs last seen in 2015. Canadian Natural Resources Ltd (CNQ.TO) fell 2.5 per cent to $45.36 and Suncor Energy Inc (SU.TO) was off 1.5 per cent at $46.93.

The materials group, which includes precious and base metals miners and fertilizer companies, lost 0.9 per cent, with Barrick Gold Corp (ABX.TO) down 1.3 per cent at $18.55 as gold prices also dipped after a recent rally. 

The two natural resource sectors combine to account for more than 30 per cent of the index's weight.

Brookfield Business Partners LP (BBUu.TO) gained five per cent to $47.35 after saying it planned to buy Westinghouse Electric Co from Toshiba Corp for US$4.6 billion. Its parent company, Brookfield Asset Management Inc (BAMa.TO), slipped 0.8 per cent to $54.16.

Marijuana producers fell early before turning higher in heavy volumes. They had been rising sharply over the last week but were hit hard on Thursday when the U.S. federal government rescinded a policy that had eased enforcement of federal marijuana laws.

Canopy Growth Co (WEED.TO) finished up 5.2 per cent at $34.00 and Aphria Inc (APH.TO) gained 3.6 per cent to $19.16. Aurora Cannabis Inc (ACB.TO) rose 2.4 per cent to $13.35 after announcing its second investment in as many days.