THIS IS THE FIRST PAGE ONLY. IF YOU WISH TO REVIEW THE ENTIRETY OF EXHIBIT “I” (REDLINED SHAREHOLDERS AGREEEMENT) CLICK HERE. EXHIBIT “I” to the order of Mr. Justice D.R.G. Thomas dated May 19, 2010 Dated for reference the [Here insert effective date...

Exhibit 99.21

THIS IS THE FIRST PAGE ONLY. IF YOU WISH TO REVIEW THE

ENTIRETY OF EXHIBIT “I” (REDLINED SHAREHOLDERS AGREEEMENT)

CLICK HERE.

EXHIBIT “I”

to the order of

Xx. Xxxxxxx D.R.G. Xxxxxx

dated May 19, 2010

Dated for reference the [Here insert effective date of Plan of Arrangement].

UNANIMOUS SHAREHOLDER AGREEMENT

CONCERNING:

PCL EMPLOYEES HOLDINGS LTD.

(hereinafter called “PCLEH”)

WHEREAS:

A. PCLEH is incorporated pursuant to the laws of the Province of Alberta.

B. The signatories hereto are all of the shareholders legal and beneficial owners of shares of PCLEH, and as such wish to define their relationship to one another and to PCLEH.

C. The shareholders legal and beneficial owners of shares of PCLEH and PCLEH wish to define their respective rights and responsibilities to sell and purchase shares under various circumstances, to create a market for the shares of PCLEH within the limits hereinafter set forth and otherwise to deal with those matters permitted to be dealt with by a unanimous shareholder agreement under the Business Corporations Act.

NOW THEREFORE THIS AGREEMENT WITNESSETH and the parties hereto mutually covenant and agree with the others as follows:

SECTION I - INTERPRETATION

Article 1.01 - Definitions:

1.01.01 In this Agreement: