Hey
I am currently planing out a Vienna Congress TL and have reached the 1860's. While the situation in my TL comes about rather differently (Murat Naples) by said point in time Austria has "drawed"/ lost two wars against France/Savoy/Murat (in different constellations). Thus funnily enough my Italy map looks almost exactly like yours (2 Italian Powers [North/South], Austria holding LV and Papal States reduced to Lazio).
With my limited understanding of the Italian unification I have identified Rome as the crucial keystone that will unite the two powers. As opposed to lets say Austria and Prussia where no single city had that kind of influence on german nationalism (Yes, Frankfurt worked for the 48' revolution, but it wouldn't work for two sovereign great powers fusing together).
So currently I am analysing butterflies to look for the next big conflict in which both Austria (obviously) and France(never underestimate French catholics in the 19th century) will be distracted and the Italians get an opportunity to take Rome.
Not wanting to spoil my TL (if I ever post it

) my Austria gets different territories out of the Vienna congress (italian provinces are almost OTL) thus changing their perception of nationalism and regional devolution. So no big italian revolts in Austria. And a small touch of "we are the superior Italians" mentality in Venetians and Lombardians, how much of that is Metternich propaganda I leave to the reader.
Now I dont know how strong and stable both of your Italian states are and what the internal situation in the great powers looks like but that are just my two cents.