Although spelled differently, McPherson Avenue is believed to be named after Sir David Lewis MacPherson.  Minister of the Interior under John A. MacDonald’s government in 1882, he was responsible for the policy of granting land to settlement companies in return for assurances of the number of settlers the companies would bring.  MacPherson gave the Temperance Colonization Society a land grant to establish their colony in Saskatoon.
From Exhibition LAP Final Report

According to historian Keith Carlson, temperance colony activist John Lake named the street in his honour after the politician intervened and stopped the surveying of long, narrow Metis river lots in the area.
Stephanie Danyluk, a historical researcher, is asking Saskatoon City Council to consider renaming McPherson Avenue, given its namesake’s “egregious” policy decisions while serving as Prime Minister John A. Macdonald’s minister of the interior.
From Saskatoon StarPhoenix, March 5 2021

Researcher Stephanie Danyluk penned a letter to City Council in which she noted
his mistreatment of Métis people asserting their land rights, citing it as a catalyst to the 1885 Riel Resistance.
From Global News, March 9 2021