Preheat oven to 400°F Grease a standard 12 muffin pan or line with paper muffin cups.
Whisk together the flour, baking powder, baking soda, cinnamon and salt in a large bowl.
In a separate bowl, whisk together eggs, sour cream, milk, sugar, butter, vanilla, juice, zest and flaxseed.
Add the wet mixture to the dry mixture, and mix together with a few light strokes, just until the dry ingredients are moistened.
Gently fold in the berries and cranberries.
Do not over-mix! Divide the batter evenly among the muffin cups. Bake at 400°F until a toothpick inserted into the middle of 1 or 2 of the muffins comes out clean, 17-20 minutes.
Let cool for 2 to 3 minutes before removing from the pan, let cool on wire rack.