How are the bike paths

There are no bike paths per se at Susquehanna State Park. It's mostly picnic area, a boat launch, and the Hiawatha Riverboat.

The river walk loop around Maynard and Market street would be a better option if looking for a dedicated bike path

Yeah not really any

The answer from John Clifford sums up the situation.

You could ride the whole park in about 10 minutes. Not a good place for riding

Your better off the path that runs along the river and Loyalsock Creek from Williamsport to Montoursville.