The Garden of the Finzi-Continis by Giorgio Bassani (1962) is the novel most associated with Ferrara — a story of a wealthy Jewish family in the city during the Fascist period, ending in the deportations of 1943. It captures the particular atmosphere of the city's Jewish bourgeoisie, its parks and tennis courts and bicycles, with an elegance that makes the tragedy all the more devastating. Bassani's other Ferrara stories, collected as The Romances of Ferrara, are equally worth reading.
The Betrothed by Alessandro Manzoni (1827) is set partly in the Po valley that surrounds Ferrara, and reading it gives context to the landscape and history of the region — the plague, the Spanish occupation, the Church — that still shapes this part of Italy.
The Italians by Luigi Barzini (1964) is not specifically about Ferrara but remains the best single account of Italian national character ever written by an Italian. Read it before any extended time in Italy.