OK: if anyone in the Prussian government has an attack of stupid this big and thanks to some miracle manages to turn such as folly into an actual proposal, Bismarck would either block it dead or reisign over it.
Let's say that the Kaiser is such an idiot that somehow he decides he really wants Corsica and manages to make his request (which includes Algeria just for the giant fuckyou value it has to France, I guess) known outside the German Cabinet. At that point, Bismarck resigns, and/or Britain makes it known that she WON'T stand for it under ANY FUCKING CIRCUMSTANCE WHATSOEVER.
Why would Britain say that?
As others have noted Prussia had no navy, so a German Algeria (or Corsica) would be less of a concern than a French one was.
As for the French, they'd agree like a shot if that was the price of keeping Alsace-Lorraine. But I agree there's no likelihood of the Germans wanting to do it.