In my opinion, you should make unpassable borders between Toscana and Emilia-Romagna, Piemonte and Liguria, Lazio and Abruzzo, molise and Campania, umbria and Marche... then you could think about the idea to connect some regions with mountain passes and to think about some main rivers like Po, Adige, Tevere, Tagliamento...
crosses all north italy from Piemonte to Veneto.. it is the natural border between
many regions, dividing Emila-Romagna
from Lombardia and Veneto
you could use Tagliamento
as well as the border between friuli-Venezia-Giulia and Veneto
then you could consider to add some bridge, in the case you need...
is the main italian lake and it is the natural border between Lombardia, Veneto and Trentino-Alto Adige
I was thinking that as 21st territory you could consider also Corsica...
and this is could be really useful, 'cause you could have the insland continent, made up by Sicilia, Sardegna and Corsica.
In fact, I suggest to divide italy into 21 territories: the 20 actual regions plus Corsica.
ideas for continents:
north-west Italy: Valle d'Aosta, Piemonte, Lombardia and Liguria
north-east Italy: Veneto, Trentino-Alto Adige and Friuli-Venezia Giulia
mid-north Italy: Emilia-Romagna, Toscana, Umbria, Marche
mid-south Italy: Lazio, Abruzzo, Molise
south Italy: Campania, Puglia, Basilicata and Calabria
"insular" Italy: Sicilia, Sardegna and Corsica
About sea route connections
Lazio should be connected with Sardegna
(and eventually also with Sicilia and Corsica)
Sicilia should be connected with Sardegna and Calabria
Corsica should be connected with Liguria and Toscana
Veneto could be connected with Puglia