Many times it's hard to find a proper word to use in casually identifying people, places, and things which are "northern nations." "Northern Italian" isn't necessarily all that accurate because that term suggests that there is a definite "Italian." The Italian Peninsula should be a regional term, like the British Isles or the Balkans. Try explaining to someone in Ireland that he's not Irish, but a "British Islander," or to people in the Balkans that they're all the same... "Balkonians!" Yet we are expected to accept the Italian-arrangement without question, despite clear evidence to the contrary. Even the Austrians didn't outlaw our language and culture.
Other terms tended to be too regional or focus on only one aspect of our history. "Subalpine" is a term, while interesting, refers more to a particular climate around the world. "Gallo-Tuscan" is okay, but is still too regionally specific for us. Of course, "Padanian," while in various forms, is a term that goes back centuries, is still identified as a very modern political term. Although we like "northern nations," it would be entirely lost upon people not of our ancestry, and it's not an adjective.
What it really boils down to is that "Padania" or "northern nations" are, to us, fine descriptive terms for a shared ancestry or a federation of former nations which are very similar; but it would still would draw criticism to throw around the Padanian name in everyday language. The best term for that, I believe, is "Cisalpine." The Romans called the land of our Gallic ancestors "Gallia Cisalpina" (Cisalpine Gaul), which meant "Gaul on this side of the Alps." Cisalpine, by itself, literally means "south of the Alps." Also, there were Celts in Tuscany and Umbria.
For our unique heritage--which is different than the much more historically unified cultures of countries like Germany, Spain, France, Poland, etc.--we require acceptable terminology. Therefore "Padania" is a good term for the modern-day Cisalpine Gaul, Etruria, or Langbard Kingdom. It should be a federation of very similar cultures from past nations, and a reference to a common heritage. However for everyday language, a less political and more regional term for description is needed: Cisalpine or Cisalpines.