Finding the cause and fighting that first is the key, then you can get I'd if the stains easily and they will be more likely to stay away.
Allergies is a common cause of tear staining, these could be environmental, but are most likely food related. Allergies in Bulldogs are common, the most common being Chicken and Grains. Salmon although not a common allergen, can cause yeast buildup, so unless this is your only other option I would avoid it.
Go for the best food you can afford, Fromms seems to be popular amongst many members here, but check the food ratings article, you can find it through the home page, for other foods that are good.
understanding food labels