The threat was issued by a member of the al Qaeda information and strategy committee, Hossam Abdul Rauf, in a document written in July, the Toronto newspaper paper said.
Rauf wrote that the Canadians "will either be forced to withdraw their forces or face an operation similar to New York, Madrid, London."
The document was obtained and translated by a US non-profit organisation, the SITE Institute, that monitors the Internet for terrorist threats, the paper said.
"Despite the strong increasing opposition to spread its forces in the fire of south Afghanistan, it seems that they (Canadians) will not learn the lesson easily," Rauf wrote.
The document condemns Canadian Prime Minister Stephen Harper for keeping troops in Afghanistan and refers to Canada's "fanatic adherence to Christianity" and its alleged attempts to "damage the Muslims" and support for a "Christian crusade" against al Qaeda.
Close to 2,500 Canadian soldiers are deployed in the Kandahar region in southern Afghanistan, fighting Taliban insurgents.

Copyright AFP (Agence France-Presse), 2006