Move a rack to the bottom third of the oven and heat the oven to 325 degrees F.
Spray the insides of the cans with nonstick spray and place set a deep 3-quart oven-safe pot. Begin heating enough boiling water to come halfway up the sides of the cans when poured into the pot.
In a medium mixing bowl, whisk together the wheat flour, rye flour, cornmeal, baking soda, baking powder, salt and allspice. Add the molasses, buttermilk, vanilla and zest and whisk to combine. Divide the mixture evenly between the prepared cans. Cover the top with a double thickness of aluminum foil and tie securely with string. Pour the boiling water into the pot. Carefully place in the oven and bake for 1 hour and 15 minutes or until the edges of the bread begin to pull away from the sides of the cans. Remove the cans from the pot of water, uncover, place on a cooling rack and cool 1 hour before removing bread from the cans. Serve with baked beans or slice, toast and serve with cream cheese.