Dig out the maps. If it looks like a secondary road, then it probably is.

I did most of my riding around Parma, and that was a few years ago, so there likely have been a few changes. Via Emilia Romagna was moderately busy, but even that wasn't too bad. But, most of the other roads between small towns were very low traffic.

I just remember the worst traffic I hit was about a 10 mile stretch near Venice, but perhaps I wasn't very good with choosing routes. Otherwise, I had a great time. My return trip from Grado back to Parma was more inland, and I got to see Verona, and one of the few active Roman coliseums.

Many of the Italian cities, at least in the plains lost their walls, but I also encountered a small walled city, Sabbioneta quite by accident on that ride.

Venice has come up a few times on Bike Forums recently.

[MENTION=228362]Gyro_T[/MENTION] went to Italy starting in Venice a couple of years ago.
Sneaking a bicycle into and out of Venice?

[MENTION=475797]paulthepyke[/MENTION] is apparently heading there this fall.
Italy September 2018

Anyway, spend some time planning your route, and then just have fun.