Take a look at s 16(1). It's triggering event is an "emergency" which is a defined event in the NDA. Unless I lost track in this meandering thread, the issue of its use was to form something in the nature of a provincial military force like the ARNG. That's an enduring organization. The s 16 Special Force is a force specifically recruited for a limited purpose - such as the Korean War. At the time DND did not want to raise more RegF or Militia troops for it and thus the Special Force provision was activated for a force that would serve for the duration of the war and then be shut down.
The OiC (which I have not read) merely incorporates the CG under DND as a special operating agency. It did not make it a component of the CAF
Well s91 of the Constitution would prevent a "military" force but there are already numerous police forces with teams armed with military gear. You're only discussing the scale of the thing. Note such a force would probably be a component of their provincial police force which for most provinces is the RCMP.
And why would the Feds want to. Maybe once the provinces started buying artillery someone might take notice.