The Toronto Stock Exchange's S&P/TSX fell 35.39 points, or 0.21 percent, to 16,527.90.
Leading the index were Cogeco Communications Inc , up 5.5 percent, Gran Tierra Energy Inc , up 3.9 percent, and Cargojet Inc , higher by 3.5 percent.
Lagging shares were Bausch Health Companies Inc , down 4.3 percent, Canopy Growth Corp, down 4.2 percent, and TORC Oil & Gas Ltd, lower by 3.7 percent.
On the TSX 77 issues rose and 155 fell as a 0.5-to-1 ratio favored decliners. There were 18 new highs and 4 new lows, with total volume of 183.8 million shares.
The most heavily traded shares by volume were Encana Corp , Canntrust Holdings Inc and Barrick Gold Corp.
The TSX's energy group fell 0.05 points, or 0.0 percent, while the financials sector slipped 0.50 points, or 0.2 percent.
West Texas Intermediate crude futures rose 0.08 percent, or $0.05, to $60.48 a barrel. Brent crude fell 0.34 percent, or $0.23, to $66.78.
The TSX is up 15.4 percent for the year.