on an ethnolinguistic perspective I would consider as northern those regions where Rheto-Cisalpine languages are spoken excluding Südtyrol (with the exception of two ladin speaking valleys) and Valle d'Aosta, although the last one is someway more "italianized" being a part of Piedmont for centuries before the italian unification. there is a small part of Valle d'Aosta which is actually piedmontese speaking and piedmontese is also spoken or understood in the rest of the region along with the franco-provençal patois. first names are generally italian:
Paginebianche.it | Risultato della Ricerca&
the average valdotaine speaks patois with the family and italian at work or outside of the family. very different if compared with Southtyrol.
one of the thing that divides the most N. Italian accent from S.Italian one is the so-called 'raddoppiamento fono-sintattico': I can't translate this expression in english but Central and Southern Italians are used to double consonants between a preposition and a word in their pronunciation
N.Italy: va bene, a volte
C. and S.Italy: vabbene, avvolte
they also double consonants inside a word: 'esagerare' becomes 'esaGGerare', 'terribile' becomes 'terriBBile'.
you can easily tell when someone is from North or South because of that.