Man, one can really get into the weeds here. The Saskatchewan Act (1905) is a federal statute considered part of the Constitution of Canada by virtue of
Section 52 (and the schedule further on). It established the province. Section 53 says the statutes listed in the schedule are repealed/amended as listed but, if not, remain in force. Nothing is indicated (in the version cited) that Act has been repealed/amended.
The
Saskatchewan Act says:
24. The powers hereby granted to the said province shall be exercised subject to the provisions of section 16 of the contract set forth in the schedule to chapter 1 of the statutes of 1881, being an Act respecting the Canadian Pacific Railway Company.
Unfortunately, I couldn't find said contract, but it seems there is general agreement that it exempts the company from
certain taxes. This should be fairly simple. A Constitutional amendment impacting on a single province is fairly straight forward, and I read somewhere that the company really isn't objecting. It doesn't seem to be huge pile of money and they'll just pass it on anyway.