No word yet on who they are playing but there is speculation in the internet that Farmiga and Bernthal may be playing Tony's parents.
Just throwing this out there: Corey Stoll as Uncle Junior? Only because he's bald. I could see Billy Magnussen, based on his looks, as a young Paulie. But who knows at this point.
The only confirmed character cast is Alessandro Nivola as Dickie Moltisante, presumably the title character. Moltisante is Many Saints in Italian.