That word ('authentic') doesn't really have much meaning in the context of Japanese restaurants in Japan - it's not like there are loads of restaurants catering to foreign tourists by offering some watered-down version of Japanese cuisine. And certainly not in Nagoya.

You might enjoy Nenohi which is near your hotel. (It's in a shopping mall, mind you, not a quaint little shack, but that's often where actual Japanese people go to eat dinner.) It's run by a sake brewery and they serve nicely prepared seasonal dishes that go with sake.

Miso tonkatsu is definitely a local Nagoya specialty, in the same way that hot dogs are a New York City specialty. But you might not want to waste your one Nagoya dinner on it.