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 tbs Grand Marnier. Glaze should have consistency of thick maple syrup. If it is too thick, thin with an additional tbs of liqueur.
Let loaves cool completely, then slice and serve, or wrap and freeze.
Chef's Notes: Loaves can be made up to 1 month ahead and frozen. Bake and glaze loaves and allow them to cool completely. Wrap tightly with plastic wrap, put in a zip-lock bag and freeze. When ready to serve, remove from freezer and defrost at room temperature.