(Reuters) - Former Canadian Pacific Chief Executive Hunter Harrison is in advanced talks to team up with a former Pershing Square Capital partner, seeking to shake up rival railroad CSX Corp (>> CSX Corporation), according to a person familiar with the matter.

Harrison on Wednesday announced his early departure from Canadian Pacific (>> Canadian Pacific Railway Limited), the railway company he led after activist fund Pershing Square tossed out the previous CEO in a 2012 proxy fight.

The Pershing Square partner who led the Canadian Pacific investment was Paul Hilal, who last year left the firm to start his own fund.

Hilal's fund, Mantle Ridge LP, has raised more than $1 billion for a single investment, according to a person familiar with the matter, with investors committed to locking up their money for five years.

The investment is expected to be aimed at CSX, with Harrison seen as playing a similar leadership role to help turn the company around as he did at Canadian Pacific, the person said.

Harrison confirmed to The Wall Street Journal on Wednesday that he and Hilal were finalizing a partnership.

CSX, Hilal and Harrison could not be immediately reached for comment.

(Additional reporting by Gayathree Ganesan in Bengaluru; editing by Sandra Maler, G Crosse)

By Michael Flaherty

Stocks treated in this article : Canadian Pacific Railway Limited, CSX Corporation