The Toronto Stock Exchange's S&P/TSX <.GSPTSE> fell 79.04 points, or 0.48 percent, to 16,462.95.
Leading the index were Birchcliff Energy Ltd , up 3.0 percent, Shopify Inc , up 2.7 percent, and Ero Copper Corp, higher by 1.9 percent.
Lagging shares were CannTrust Holdings Inc, down 22.6 percent, SNC-Lavalin Group Inc, down 6.3 percent, and Precision Drilling Corp, lower by 4.5 percent.
On the TSX 72 issues rose and 161 fell as a 0.4-to-1 ratio favored decliners. There were 4 new highs and 3 new lows, with total volume of 170.2 million shares.
The most heavily traded shares by volume were Canntrust Holdings Inc, Toronto-dominion Bank and Encana Corp.
The TSX's energy group <.SPTTEN> fell 1.08 points, or 0.8 percent, while the financials sector <.SPTTFS> slipped 1.24 points, or 0.4 percent.
West Texas Intermediate crude futures fell 0.05 percent, or $0.03, to $57.48 a barrel. Brent crude fell 0.5 percent, or $0.32, to $63.91 [O/R]
The TSX is up 14.9 percent for the year.