The Toronto Stock Exchange's S&P/TSX composite index ended down 111.74 points, or 0.5%, at 20,490.36, its lowest closing level since Aug. 23.

For the week, the index was down 0.7%, extending its pullback from a record high earlier this month.

"I think a lot of Canadians are looking to the election on Monday," said Allan Small, senior investment adviser of the Allan Small Financial Group with iA Private Wealth.

Equities investors are casting a nervous eye over some of the campaign promises made by Canadian political parties, including Prime Minister Justin Trudeau's vow to raise corporate taxes on the most profitable banks and insurers to help pay for the cost of the economic recovery and his pledge to immediately cap oil and gas emissions.

The financial services sector, which accounts for about 30% of the TSX's valuation, fell 1%. Energy was down nearly 2% and the materials group, which includes precious and base metals miners and fertilizer companies, lost 0.7% as commodity prices fell.

Oil settled 0.9% lower at $71.97 a barrel, while copper was down 0.7%.

Investors "are kind of taking a wait-and-see approach because September is normally a soft month," Small said. "If there is no good news it seems the path of least resistance is lower."

U.S. stocks were also lower in a broad selloff.

Canadian National Railway Co gained 2.4% after the railroad operator said it would resume a previously approved share buyback, days after walking away from its $29.6 billion deal for U.S. railroad operator Kansas City Southern.

(Reporting by Fergal Smith in Toronto; Additional reporting by Amal S in Bengaluru; Editing by Matthew Lewis)

By Fergal Smith