Headcanon: not a plain white loaf, but a good solid brown bread, probably even with a certain amount of bean and vegetable flour worked in but only enough for flavoring; a true artisan loaf but not so flashy as to seem like a real theft-level crime to a poor peasant looking for a meal
Heartcanon: while it was never returned to its original owner, another one of the village’s poor children found it where it had fallen after Valjean dropped it, and took it to share with their family, because Something Something Providence
Gutcanon: probably a round loaf instead of a long baguette type
Spleencanon: was eaten as bread and not mushed together with a hundred other food and non-food substances into some horrific monster gruel Hugo