Saad al-Jabri was a long-time aide to Prince Mohammed bin Nayef. The crown prince - known as MbS - ousted Nayef as heir to the throne in a 2017 palace coup that left him the de facto ruler of Saudi Arabia, a close U.S. ally.
People with knowledge of the situation told Reuters earlier this year that Jabri has access to documents containing sensitive information that MbS fears could be compromising.
In a 107-page lawsuit against MbS and 24 others filed in federal court in the District of Columbia, Jabri said the crown prince "dispatched a hit squad" to Canada in October 2018.
"(A) team of Saudi nationals traveled across the Atlantic Ocean from Saudi Arabia ... with the intention of killing Dr. Saad," said the lawsuit, which seeks punitive damages in an amount to be determined at trial.
The Saudi government media office did not immediately respond to a request for comment on the lawsuit. The Saudi embassy in Ottawa was not immediately available for comment.
The "hit squad" was comprised of members of a group close to MbS called the Tiger Squad, and they carried two bags of forensic tools and included someone who knew how to clean up crime scenes, according to the lawsuit.
The men "attempted to enter Canada covertly, traveling on tourist visas" and pretending not to know each other. Suspicious border agents found a photo showing several of the men together, "revealing their lie and thwarting their mission," it said.
The alleged incident took place less than two weeks after Saudi agents murdered journalist Jamal Khashoggi in the kingdom's Istanbul consulate. Turkish sources told Reuters a bone saw was used to dismember the journalist.
MbS came under international criticism over Khashoggi's killing, which U.S. government sources say the Central Intelligence Agency believes MbS approved and may have ordered.
The crown prince has denied ordered Khashoggi's killing but said he ultimately bears "full responsibility" as the kingdom's de facto leader.
Jabri's family says MbS has detained two of his adult children and his brother to try to force his return.
Jabri, who described himself as a long-time ally of U.S. intelligence services, said he filed the suit in the United States in part because the alleged plot against him "involved substantial conduct inside the United States."
The office of Canadian Foreign Minister Francois-Philippe Champagne referred queries on the matter to the office of Public Safety Minister Bill Blair, which did not respond to a request for comment.Canada's relations with Saudi Arabia have been poor since August 2018, when Ottawa criticized Riyadh over human rights.