The Toronto Stock Exchange's S&P/TSX fell 123.64 points, or 0.74 percent, to 16,488.20.
Leading the index were Mullen Group Ltd , up 8.6 percent, FirstService Corp , up 2.8 percent, and Aritzia Inc , higher by 2.8 percent.
Lagging shares were Cameco Corp , down 7.6 percent, Nexgen Energy Ltd, down 6.2 percent, and OceanaGold Corp, lower by 6.2 percent.
On the TSX 60 issues rose and 176 fell as a 0.3-to-1 ratio favored decliners. There were 9 new highs and 7 new lows, with total volume of 209.3 million shares.
The most heavily traded shares by volume were Enbridge Inc , Suncor Energy Inc and Encana Corp.
The TSX's energy group fell 3.96 points, or 2.9 percent, while the financials sector slipped 0.89 points, or 0.3 percent.
West Texas Intermediate crude futures were flat percent, or $, to $55.88 a barrel. Brent crude fell 0.13 percent, or $0.08, to $63.1.
The TSX is up 15.1 percent for the year.