Assuming that the design – certification standard of the autoflight system meets the requirements in CS AWO 300 and CS25 (AC 29 / FAR25), then the operating requirements (EU-OPS, FAR121) generally determine both the minimum RVR and the land/GA options for the crew.
Cat 3A does not necessarily require autoland; see CS-AWO 321.
For 50 ft DH (Cat3A) in RVRs greater than 200m (may vary by aircraft type), where the crew have and can maintain the required visual references and the aircraft is on a stable flight path, etc, etc, then the crew can continue to land.
However, a manufacturer/regulator can impose an operating limit requiring a GA if the aircraft handling / workload / flight deck view / system characteristics etc for continued landing warrants it.
One difference to the above, particularly in Europe, is if the aircraft/autoflight system is certificated as ‘highly reliable fail passive’ enabling reduced RVR operations ~ 150m, then a mandatory GA would probably be required.
EASA Certification Specifications
Agency Measures | Certification specifications