Preheat Oven: Preheat to 350°F (175°C) and grease a standard loaf pan.
Mix Wet Ingredients: In a bowl, whisk sugar, eggs, sour cream, canola oil, lemon zest, lemon juice, and vanilla extract until smooth.
Prepare Dry Ingredients: In another bowl, sift flour, baking powder, and salt.
Combine Mixtures: Gradually mix the dry ingredients into the wet ingredients until just combined.
Cream Cheese Mixture: Beat cream cheese and powdered sugar until smooth.
Layer Batter: Pour half the batter into the loaf pan, dollop half the cream cheese mixture on top, and gently swirl with a knife. Repeat with remaining batter and cream cheese.
Bake: Bake for 65-70 minutes, covering with foil if the top browns too quickly. Check doneness with a toothpick.
Cool: Let the loaf cool completely before slicing and serving.