Preheat oven to 350°F. Set aside a 12-cup bundt pan but don't grease it just yet.
In a medium bowl, whisk 3 cups flour, baking powder, baking soda, and salt, set aside. In a liquid measuring cup, combine buttermilk and lemon juice, set aside.
Using a stand mixer fitted with the paddle attachment, beat the butter, oil, sugar, and lemon zest until combined. With the mixer on a low speed, add the eggs one at a time, scraping down the bowl between each addition, followed by the vanilla extract.
Add half of the flour mixture to batter, beating until just combined. Beat in the buttermilk-lemon juice, followed by the remaining flour, scraping the bowl as needed.
In a separate bowl, toss the blueberries with two tablespoons of flour. Gently fold the berries into the cake batter.
Thoroughly and generously grease a 12-cup bundt pan. I find that nonstick baking spray with flour works the best for this. Scoop the batter into the prepared pan and smooth the top. Bake for 40-50 minutes, until a toothpick inserted into the cake comes out clean.
Set the cake pan on a wire rack to cool for 30 minutes. Meanwhile, prepare the syrup.