The reported offer comes months after Canadian Pacific refused to raise its bid for Kansas City Southern, with the U.S. company saying that Canadian National Railway's offer was "superior".

Shares of Kansas City Southern were up about 6% in aftermarket trading.

Canadian Pacific and larger rival Canadian National have been in a race to acquire Kansas City Southern, which would create a North American railway spanning the United States, Mexico and Canada, as supply chains recover from pandemic-led disruptions.

Canadian Pacific's raised offer could kickstart a takeover battle for the U.S. railroad operator.

WSJ reported Canadian Pacific could raise the offer to $300 per share from its initial offer of $275 apiece.

The headline price in Canadian National's cash-and-stock bid is $325 per share as originally announced.

Kansas City Southern declined to comment when contacted by Reuters, while Canadian Pacific and Canadian National did not immediately respond.

(Reporting by Shreyasee Raj; Editing by Shailesh Kuber)