CP will today outline a recovery plan to investors and analysts, while at the same time presenting a critique of what it describes as Pershing Square's misguided turnaround strategy. CP says its plans to improve efficiency are regarded as realistic by consultancy Oliver Wyman, while Pershing Square's targets are unrealistic.

"It's not the way one would want to proceed, but I think in light of the serious, serious flaws in the Pershing analysis, it's my responsibility to the CP shareholders to make sure that they understand they've been misinformed," says Green.

CP has twice invited Ackman to become a board member, but Ackman intends to propose his own team of six directors at CP's annual meeting on May 17.