As for CP/Soo's maintaince record, well CP has long been known for having great maintainance especially for locomotives. They kept engines going that had long been scrapped by their other owners, the F-M C-Liners, H-Liners and Trainmasters were used into the 1970s and the MLWs were on road until the 1990s.
They also kept a very sizable fleet of 40' boxcars going for a very long time, again up into the 1990s. Some of these cars were used in grain service on docks that were built too light for modern covered hoppers.
Now as for Soo, having grown up in Milwaukee, I've seen Soo my whole life. While I do not know offhand any numbers and figures regarding their mantainance and how much was differed, I do know they followed their parent's tradition of keeping first generation power going long after the expected service life. I remember seeing high-nosed Geeps back in the 1990s, switching in the valley, and while they were rather ragged and not nearly as clean or rust-free as the CP units, they did work, hard.
A lot of the more run-down equipment came to the Soo by way of its aquiring of the Milwaukee Road, which had run much of its equipment into the ground in efforts to save money. In my meandering observations, and I'm by no means an expert, it seemed my view that the Soo never really recovered from eating the Milwaukee, then again it was only a few years until they were fully merged into the CP.
Today, Soo seems to be integrating into the CP well, their SD-60s are pulling alongside CP AC4400s. CP still has yet to repaint a lot of the Soo (and for that matter the old Milwaukee) equipment, if they ever will. The Soo SD60s I believe are all still painted either with the Hockey Stick red and white or in Candy Apple Red.
Cheers!
~METRO