The focaccia di Novara is the odd one out: it is sweet. Novara sits in Piedmont rather than on the Ligurian coast, and its focaccia belongs to the family of soft, enriched sweet breads rather than to the oiled, salted flatbreads that share the name elsewhere. The dough is enriched and lightly sugared, baked into a soft, tender, slightly domed loaf rather than a thin dimpled disc, and finished plain or with a sugared top rather than with salt brine and olive oil. It is a thing eaten with coffee or at the end of a meal, not split at a counter and filled. Calling it a focaccia is a regional use of the word, and the gap between this and a Genovese round is the gap between a sweet breakfast bread and a savory street food.
That sweetness is the reason it does not function as a sandwich in the way the coastal focacce do. There is no salt-and-oil surface to season a filling, no absorbent crumb built to take on tomato or cured meat, and the sugar in the dough fights anything savory pressed into it. Where it does behave like a sandwich is in its own sweet register: split and spread with butter, or with a soft fresh cheese, or filled with a little jam or a slice of seasonal fruit, the enriched crumb doing the same supporting work a brioche would. The tender, close texture holds a soft spread without tearing and stays pleasant at room temperature, which is how it is usually eaten, in slices, with something to drink.
The named relatives that actually share its method are sweet rather than savory, and the savory focacce that share only its name belong to a different tradition entirely. The dimpled, salted Genovese round and the lean coastal styles like Noli and Voltri are a separate subject. The sweet Piedmontese and Lombard enriched breads it sits beside each have their own treatment and deserve their own articles rather than being crowded in here.