For the syrup: Combine the sugar and orange juice in a medium high-sided saute pan over high heat and cook until caramelized, about 2 minutes; do not stir. Whisk in the butter and vanilla extract until melted. Stir in the oranges and zest.
For the French toast: In a baking dish, whisk together the eggs, cream, milk, orange juice, vanilla extract, orange zest and salt until combined. Soak the bread slices in the egg mixture until completely soaked through, at least 15 seconds per side.
Heat 2 tablespoons butter and 1 tablespoon oil in in a large saute pan over medium-high heat until it begins to sizzle. Add 3 slices bread at a time and cook, turning once, until golden and crisp on both sides, about 2 minutes per side. Repeat with the remaining bread.
Serve the orange marmalade syrup over the French toast.