(New throughout, updates prices and market activity, adds comment from portfolio manager, details on index and stocks)
* TSX closed down 75.68 points, or 0.55 percent, at 13,632.00
* Five of the TSX's 10 main groups ended lower
By Fergal Smith
TORONTO, May 4 (Reuters) - Canada's main stock index fell to a two-week low on Wednesday as resource and financial stocks lost ground, while domestic trade data disappointed and a wildfire led to production cuts in the country's oil sands region.
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 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 fell 3.6 percent to C$22.48, while First Quantum Minerals Ltd was down 8 percent at C$9.29.
Spot gold fell 0.5 percent, retreating further from a 15-month high as the U.S. dollar rose, while copper prices declined 1.1 percent to $4,867.15 a tonne.
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 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 prices settled at $43.78 a barrel, up 0.30 percent, although some gains were pared after a bigger-than-expected build in U.S. crude inventories offset production cuts in Canada.
Financial stocks fell 0.6 percent. It included a 1.3 percent decline in the shares of Bank of Nova Scotia to C$62.61.
Canadian National Railway Co 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 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)