I can confirm that the Shimano Deore XT cantilever brakes work well on a loaded or unloaded tandem with road levers, Dyad rims, 32-37mm tires, and 52mm fenders. The initial setup is slightly time consuming (as with any cantilever brake). They hold their adjustment well enough that we could wear through cartridge brake pads and only adjust the cable barrel adjuster. (As an aside) I wish I could say the same about my Avid BB7 with 203mm rotor.
The Paul Neo Retros would be fine too. Stoker heal clearance or pannier clearance could be an issue with the Neo Retros.