This is kind of to my point as well since MP are a support unit and not a main regiment, Calvary is gonna still be expensive in a sense and mostly pointless if no divisions spawn for them to whack-a-mole (Not saying I want that) so I'd rather just have a MP as a division I can create or maybe instead of Calvary have Light Infantry regiments.
How about this kind of template for the MP division:
1x MP support battalions
2x regiments of 2x infantry battalions each
And in case an amphibious assault happening nearby, you upgrade the police division nearby to a more front line oriented template, so that it can support to contain and defeat the bridgehead.
Edit: Changed the number of MP battalions, because I have been made aware that only one type of support battalion is allowed per division. Thank you kviiri.
Edit2: My idea here is to have a dual role division. One role with little fighting power (to conserve equipment and manpower) that can suppress the resitance, but that can also be converted/mobilized to counter amphibious/airborne raids/assaults. Maybe it can be downsized after the assault has been repelled, so that the equipment and manpower is being pooled again. I do not know though if this is allowed in the template/division planner.