... Be safe in knowing that if it was a national security matter all the stakeholders would be talking to one another.
Now are you wondering if a Cpl in a Reserve unit would be in the DND loop like an episode of E-ring or 24??.. um ah No..
(chuckle) - the only thing that could have improved upon your post would have been to mention "... an episode of JAG ..." (LOL) - the other exception being ... when reservists are police officers on civvie street (!)
Bloggins also made a very, very good post - good on you! (although, I'm thinking we need to underline and bold "limited CSS")
On a normal/ongoing basis, information is passed within police circles - municipal/regional police will share with provincial/federal levels, and then the RCMP has input into a larger loop up in Ottawa - that's where Other Government Departments (OGD) get informed, as appropriate/necessary (including DND).
As an aside, civilian police forces also have some interface on a daily/lower level, when it comes to Explosive Ordnance Disposal (EOD) - however, that's largely mundane (i.e. you'll never see it on E-ring, 24 or JAG).