The investment will fuel Rockefeller's ambitions to double client assets in three to five years from a current $100 billion.

"We've got a significant opportunity" to grow in the U.S., Rockefeller CEO Gregory Fleming told Reuters in an interview.

"Our core focus is on advisers," he added, referring to its current wealth managers and potential new hires who would help to expand the company's 44 offices in the U.S.

Rockefeller manages money for the eponymous family and other ultra-high net worth clients. The new IGM stake brings the backing of another wealthy family, the Desmarais, in Canada. Viking Global Investors remains Rockefeller's biggest shareholder.

The deal negotiations began in the fall, despite a softening economic outlook, Fleming said. The payment to Rockefeller is due on June 2, IGM said in a statement.

"Purchasing an ownership stake in Rockefeller is a risk-smart entry to the U.S. market," IGM CEO James O'Sullivan said. "It has the potential to drive meaningful earnings growth for IGM over time."Fleming is an industry veteran who previously led Morgan Stanley's wealth and investment management arms. As chief operating officer of Merrill Lynch, he helped steer the Wall Street firm through the financial crisis and its acquisition by Bank of America in 2008.

(Reporting by Lananh Nguyen; Editing by Jamie Freed)

By Lananh Nguyen