I am currently shooting with the 36MP Nikon D810 for landscapes. If I were to jump ship to print big for landscapes, I would move to the Fuji GFX 100S (100MP medium format digital sensor). Staying with Nikon, the D9 or Z7II would be desired. (I am not worried about Nikon disappearing) No slouches on the Nikon Z glass, but you could still use your F-mount glass with the adapter. In the Canon venue, I'd consider the R5. The eye detection in the Canon R and Nikon Z would be nice for wildlife and people. Per DXO, not much real-life difference between the sensors of the Canon R, Nikon, Z and Fuji A7R. I would choose the best that fits your budget and purpose.