UPDATE 1-Guay tapped as new head of Caisse de depot

(Adds details, background)

TORONTO, Sept 5 (Reuters) - Caisse de depot et placement du Quebec named Richard Guay president and chief executive on Friday, replacing Henri-Paul Rousseau who stepped down earlier this year.

Guay, who joined the Caisse in 1995 and became chief financial officer in March 2006, had been acting as interim CEO of the country's largest pension fund manager since May 30.

Rousseau, who had been with the Caisse since September 2002, will join Montreal-based holding company Power Corp of Canada (POW.TO) and its Power Financial Corp (PWF.TO) unit as vice-chairman on Jan. 1.

The Caisse manages some C$155 billion ($145.6 billion) in net assets for various pension and insurance plans, making it one of the largest institutional investors in North America. ($1=$1.06 Canadian) (Reporting by Scott Anderson; editing by Rob Wilson)