Perhaps it would be fairer to say that there would/should be resistance to cancelling one if the other wasn't too, and the other isn't going.
I just reflexively resist the notion that such services are frozen in amber like the Constitution because it's too hard to choose to improve them or discard them. It's not like CPKC are going to anything other than wave goodbye to have the inconvenience of 185/186 removed. Similarly if 185/186 is stopped without replacement, presumably the feds simply zero that obligation as when they were subsidizing the old Northlander. Meanwhile Ontario is dropping huge sums on new equipment for Northlander for a route which unquestionably has road access. As I have complained previously, there is a frustration in being unable to objectively figure out what is worth keeping/adding/discarding.
As for White River-Sudbury I would see not as a standalone as it basically is now, and having to stand or fall on that basis, but as part of Toronto-Sudbury-Thunder Bay transportation options. Unfortunately it seems to be similarly quick at present to get an ONTC bus White River-Sault-Sudbury (617km) as the VIA train (268 rail miles, 431 km). Unless there is some way to improve that, it's unlikely to be offered in route planning systems.