Tear eight 14-inch pieces of nonstick foil and lay them out nonstick-side up.
Brush the centers of each piece with the melted butter.
Whisk together the evaporated milk, eggs, maple syrup, vanilla and cinnamon in a small baking dish or large resealable bag.
Dip each side of each piece of bread in the milk mixture until fully submerged.
Arrange 2 pieces of bread next to each other, without overlapping, on 1 piece of buttered foil.
Repeat with the remaining bread and 3 pieces of foil.
Make the foil packs: Put the remaining 4 pieces of foil, buttered-side down, directly on top of the bread so the foil touches the bread and the edges line up.
Fold and crimp the edges tightly to make 4 oblong packets.
Put the packs on the grill, close the lid and cook for 5 minutes.
Turn the packets over, close the lid and grill 5 minutes more.
Remove and let rest for a few minutes.
Carefully open the packets (hot steam will escape).
Both sides of the French toast should be browned and the center should be custardy.
Keep in the packets or transfer to plates.
Top each serving with 1/4 cup of the berries and more maple syrup, if desired.