September futures on the S&P/TSX index were down 0.6% at 7:01 a.m. ET (11:01 GMT).
Fitch surprisingly cut the coveted U.S. government's credit rating by one notch to AA+ from AAA on Tuesday, citing fiscal deterioration.
The Fitch downgrade pushed gold prices higher as the U.S. dollar and Treasury yields slipped, souring confidence in the American economy and shoring up interest in safe-haven bullion.
Metal prices also dropped on weak demand outlook from top consumer China after poor economic data.
Oil prices surged, trading near their highest levels since April, buoyed by crude and fuel product inventory data that showed robust U.S. demand.
The Toronto Stock Exchange's S&P/TSX composite index ended 0.5% lower on Tuesday.
Thomson Reuters Corp, on Wednesday reported higher sales and operating profit in the second quarter, helped by strong performance at its "Big 3" segments: Legal Professionals, Corporates and Tax & Accounting Professionals.
Bausch + Lomb posted modestly better than expected second-quarter earnings on Wednesday after its new chief executive, Brent Saunders, took the helm in March.
Canada is set for an earnings-heavy week, as the world's biggest fertilizer producer Nutrien and solid waste services company Waste Connections are due to report quarterly results later in the day.
COMMODITIES AT 7:01 a.m. ET
Gold futures: $1,960; +0.5%
US crude: $82.03; +0.8%
Brent crude: $85.49; +0.7%
(Reporting by Siddarth S in Bengaluru; Editing by Milla Nissi)