Preheat oven to 330°. Butter two 6-cup-capacity loaf pans (or, if making the mini loaves, butter six 2-cup-capacity pans.
With an electric or standing mixer on medium speed, cream butter and sugar together in a large bowl until pale and fluffy, about 3 minutes. Add eggs one at a time, mixing well after each. Add orange juice, sour cream, orange zest, and vanilla; mix until blended.
In a separate bowl, whisk together flour, baking powder, and salt. Add flour mixture and cranberries to wet ingredients and mix just until dry ingredients are absorbed; do not overmix.
Pour batter into prepared loaf pans. Bake until a toothpick inserted in centers of breads comes out clean, 70 to 75 minutes for large loaves and 60 minutes for mini loaves.
Meanwhile, in a small bowl, whisk together powdered sugar and 7 tablespoons Grand Marnier. Glaze should have consistency of thick maple syrup or corn syrup. If it is too thick, thin with an additional tablespoons of liqueur.
Let loaves cool in pans for 10 minutes, then remove and transfer to a cooling rack set over a large baking sheet. With a thin skewer or long toothpick, poke deep holes in tops of loaves. Drizzle with Grand Marnier glaze so that it coats the top, runs down the sides, and seeps through the holes.
Let loaves cool completely, then slice and serve, or wrap and freeze.