The index weakened for a third straight day, extending a pullback from Friday's six-month high of 13,972.62.
"We have relatively stretched valuations and I think just a lot of (investor) repositioning from the upswing we've had on the commodity side," said Ben Jang, a portfolio manager Nicola Wealth Management.
The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> closed down 75.68 points, or 0.55 percent, at 13,632.00. Five of the index's 10 main groups ended lower.
Still, the index has rebounded 18 percent from a nearly 3-1/2-year low in January, helped by a rebound in commodity prices.
The materials group, which includes precious and base metals miners and fertilizer companies, lost 2.4 percent.
Barrick Gold Corp (>> Barrick Gold Corp.) fell 3.6 percent to C$22.48, while First Quantum Minerals Ltd (>> First Quantum Minerals Limited) was down 8 percent at C$9.29.
Spot gold
Energy stocks fell 0.7 percent after a wildfire in the heart of the Canadian oil sands region disrupted oil company operations.
Suncor Energy Inc (>> Suncor Energy Inc.) declined 2.2 percent to C$34.18. The company said it was reducing crude production in the oil sands region to allow employees and families to get to safety.
U.S. crude
Financial stocks fell 0.6 percent. It included a 1.3 percent decline in the shares of Bank of Nova Scotia (>> Bank of Nova Scotia) to C$62.61.
Canadian National Railway Co (>> Canadian National Railway Company) lost 2.1 percent to C$75.93, while the overall industrials group ended down 0.5 percent.
Canada's trade deficit widened in March to a record C$3.41 billion as exports sank for a second month on weak demand from the crucial U.S. market.
Shares of Maple Leaf Foods Inc (>> Maple Leaf Foods Inc.) jumped 6.8 percent to C$28.03 after the meat processor reported a better-than-expected quarterly profit, helped by higher earnings in its prepared meats business.
The overall consumer staples group rose nearly 1 percent, while defensive telecom stocks rose 0.8 percent.
(Reporting by Fergal Smith; Editing by James Dalgleish and David Gregorio)
By Fergal Smith