Financial stocks led declines as bond yields fell, while gold miners gained and energy stocks perked up with a surge in oil prices and news of a deal in Alberta's oil patch.
Teck Resources Ltd (>> Teck Resources Ltd) fell 6.7 percent to C$29.47 after Chinese sovereign wealth fund China Investment Corp, a cornerstone shareholder, sold a substantial chunk of its holding.
The diversified miner had risen steadily from a trough below C$20 in mid-June as copper prices lifted off.
The heavyweight financials group lost 1.2 percent, tracking larger losses among U.S. financials as investors flocked to low-risk government debt in reaction to North Korea's biggest nuclear missile test yet.
"People are getting a little bit nervous about the approaching debt ceiling in the U.S., and certainly North Korea has rattled people significantly," said Rick Hutcheon, president and chief operating officer at RKH Investments.
The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> ended down 101.45 points, or 0.67 percent, at 15,090.15.
The most influential movers included Royal Bank of Canada (>> Royal Bank of Canada), which fell 1.5 percent to C$90.77, and insurer Manulife Financial Corp (>> Manulife Financial Corp.), down 2.6 percent to C$24.01.
The energy group edged 0.4 percent higher as crude prices jumped and gasoline slumped with refineries in Texas starting to resume operations in the wake of Hurricane Harvey. Another hurricane, Irma, is rolling toward the southern United States.
"No one knows where Irma is going to go, the track looks like it's through Florida but it could go right back into Texas again," Hutcheon said.
Canadian Natural Resources (>> Canadian Natural Resources Limited) gained 1.5 percent to C$39.30 after agreeing to buy Cenovus Energy's (>> Cenovus Energy Inc) Pelican Lake heavy oil operations in Alberta for C$975 million ($787 million). Cenovus shares jumped 3.3 percent to C$10.28.
Eight of the index's 10 main groups finished in negative territory, with decliners outnumbering advancers by a 1.5-to-1 ratio overall.
The materials group, which includes precious and base metals miners and fertilizer companies, gained 0.2 percent as gold miners were boosted by a jump in the precious metal to a one-year high, offsetting Teck's fall.
Kinross Gold Corp (>> Kinross Gold Corporation) gained 4.7 percent to C$5.81 and Goldcorp Inc (>> Goldcorp Inc.) rose 2.3 percent to C$17.41.
Hudson's Bay Co (>> Hudson's Bay Co) fell 6.8 percent to C$11.27 as investors braced for its earnings report after the bell.
(Reporting by Alastair Sharp; Editing by Nick Zieminski and Leslie Adler)
By Alastair Sharp