I don't know how to treat the canister for winter, but i can tell you what the holes are for.
As you are facing the pool with the canister at your feet:
bottom hole closest to the pool: usually not used, may have a short piece of pipe glued into it to be able to glue a cap onto it
Bottom hole closest to your feet: That line goes back to the pump (filter).
Top hole nearest to pool: Goes right into the pool. If you look over the edge of the pool you can see this line (equalizer).
Two side holes at the top: One goes to the main drain, and one may go to the skimmer rear hole (if its a one pump system). If not, it's capped off.
Note: This is how Paramount wants the pool builder to plumb the system. However, If the pool builder thinks there is a better way to plumb it,
...what i have told you may not be accurate.
Once you get your pool drained down, you can verify by running water (garden hose) thru the holes and see where you get water.
