Based on this reddit thread:
It looks like the 3-day/4-day Magnifica itineraries will be swapped with the Seascape, hence why all the Seascape bookings were canceled. So the Seascape stays in Miami, doing short Ocean Cay + Bahamas + Key West cruises.
Given that the Magnifica ends its World Cruise in Marseilles, I'd assume they'll keep the Magnifica in the Western Med for Summer '25.