William Ackman’s Pershing Square Capital Management LP, Canadian Pacific Railway Ltd.’s largest shareholder, urged the carrier to hire the former chief executive officer of rival Canadian National Railway Co., a person familiar with the matter said.

Pershing recommended to Canadian Pacific’s board that CEO Fred Green be replaced with Hunter Harrison, who led Canadian National from 2003 through 2009, said the person, who asked not to be identified because the details are private.

Ed Greenberg, a spokesman for Calgary-based Canadian Pacific, declined to comment today to Bloomberg News. Jennifer Burner, a spokeswoman for New York-based Pershing, couldn’t immediately comment.

The Globe & Mail reported on the discussions earlier today.