Check FAR 91.175:
[(c) Operation below DH or MDA. Except as provided in paragraph (l) of this section, where a DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, at any airport below the authorized MDA or continue an approach below the authorized DH unless-- ]
(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;
(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and
(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.
(ii) The threshold.
(iii) The threshold markings.
(iv) The threshold lights.
(v) The runway end identifier lights.
(vi) The visual approach slope indicator.
(vii) The touchdown zone or touchdown zone markings.
(viii) The touchdown zone lights.
(ix) The runway or runway markings.
(x) The runway lights.
[(d) Landing. No pilot operating an aircraft, except a military aircraft of the United States, may land that aircraft when--
(1) For operations conducted under paragraph (l) of this section, the requirements of (l)(4) of this section are not met; or
(2) For all other part 91 operations and parts 121, 125, 129, and 135 operations, the flight visibility is less than the visibility prescribed in the standard instrument approach procedure being used.
What you're missing is that the *effective* MDA is actually the DDA (Derived Decision Altitude) which is MDA + 50'.
Let's say the MDA is 500' baro. Add 50' for a new DDA of 550' baro.
Unless you can set 550' in your altitude alerter, you would have to round up to 600', giving up another 50'.
If your AP starts the altitude capture at say....around 650' baro, you've now given up *another* 50' and committed yourself to a missed approach.
In our airline, the pilot monitoring would call "minimum, approach lights/runway in sight" at 550' on the altitude tape, PF would disconnect, (the airplane still trimmed and descending), and you would continue manually to the runway.
I'm not understanding why an an autopilot-controlled level-off would be beneficial to any crew using CANPA procedures other than to make arses and elbows out of an already complex procedure.