[mullingitover]

Per the wiki article I linked, they are actually federal police officers, it's just that Canadian Pacific appoints them:

> They are duly appointed and armed federal police officers that gather their authority in Canada via the Railway Safety Act as well as other acts.

Canadian Pacific is nearly 150 years old, I would bet that the Canadian government didn't want to be on the hook for policing such a massive geographic footprint for a private business, but at the same time did want to ensure that an industry that was vital to national security was secured. The alternative was probably nationalizing the entire business, which they likely also didn't have the stomach for.