Those defences necessary to defend the coasts. Conceivably a mix of artillery assets mounted on ships belonging to the RCN, artillery assets launched from fixed and mobile platforms belonging to the army and artillery assets mounted on aircraft belonging to the RCAF.
The only currently viable coastal defences we have are those belonging to the RCN and those belonging to the RCAF. I would argue that the the RCAF is the only viable player given that its fleet generally plays at home while the RCN plays away.
The artillery assets in common to the RCN, RCAF and Army are bullets, shells, bombs and rockets with an assortment of guidance systems ranging from the non-existent to 1m CEP.
Externally powered munitions, like bullets, shells and bombs, have limited range, poor accuracy and demand complex launching systems. Self-powered munitions, like ballistic rockets, jet powered cruise missiles, UAVs, Loitering Attack Munitions and Precision Guided Munitions are often platform independent and can be launched from aircraft, ships, barges, submarines, trucks, trains and concrete pads. Many of them can skip the complexity associated with aircraft and airfields, cruisers, carriers and submarines by virtue of their range or the availability of a simple long range booster UAV that can be strapped on.
The AOPS and MCDVs can be protected by anti-air and anti-ship missiles, as well as bullets, delivered by RCAF F18s and F35s. Conceivably they could also be protected by CP-140s and P8s as well as RPAS if they were fitted to carry and launch munitions currently in Canadian inventory or planned. Those same munitions could also be delivered from terrestrial launchers, presumably under the control of the Canadian Army.
Making those launchers available for home, or coastal defence, covering the approaches currently covered by F18s, C130s and CH-149s, would release the RCN for distant waters missions in support of foreign affairs and national diplomacy.
The AOPS is more likely to spend time observing than it does attacking or defending. If it can maintain a stand-off by virtue of its own fleet of UxVs or by UxVs operated by partners in the patrol zone then the question becomes how quickly can a suitable munition be supplied from shore to eliminate an identified threat. Sea going threats take days to cover the same distance that an aircraft, crewed or uncrewed, can cover in hours.
I would say that based on current realities then the main gun of the AOPS might be upgraded to manage a primary C-UAS role with surface engagement being a secondary task.