I'm not affiliated with this shop in any way--I just stumbled upon it the other day. But, for Americans who are newly arrived or craving a bit of home, there's a place called Mickey's House on Rue Centrale between Globus and the Bessière metro stop that has three tiny rows of American processed food.
On a quick stroll through, I saw Kraft mac & cheese, creamed corn, quick grits, cranberry sauce and tons of candy. It's all gross, but if you have kids clamoring for a taste of home, it might help. Fair warning, the prices are what you would expect.
(I looked for brown sugar but no joy). http://www.mickyshouse.ch/shop/fr/57-epicerie-fine