I think your 100% cranberry juice wine will be way too tart, there's a LOT of acid(s) in cranberries & when all the sugar is fermented out it'll be super-tart; I found that out with prune juice. You might want to add some water to that juice before starting your primary fermentation.
There MIGHT be an upside to this though. I recently discovered a cherry/apple/black currant wine I made that was super-tart from the black currants had mellowed with age, that tartness had aged out. Now I haven't yet tasted my prune juice experiment, but I now have some hope that it too will eventually be drinkable, maybe even really tasty. The drawback to this is that it takes a long time for that super-tartness to mellow with age. I suppose you could always backsweeten & stabilize if you wanted to speed things up. Regards, GF.