FMS has nothing to do with CANPA.

In it's basic form you simply calculate a vertical speed (based on ground speed) from the FAF (or other appropriate descent point) that will give you a glide path which will get to MDA (we add 50' so we don't bust it) at about the MAP. You still have to clear intermediate step downs, but in almost all cases you will if you do it right. The FAA doesn't usually publish step downs that are too far outside of a "normal" approach angle...that would make for unstabilized approaches.

Yes, you can use it on a LOC or other non-prec approach, that's what it's for...no need for CANPA on an ILS or other approach with vertical guidance.

You can do a steep descent to get down early but then you have to level off...the ideal way to do a CANPA is to arrive at MAP or VDP almost at MDA so you either continue the descent or go missed.