Preheat the oven to 350°F (175°C). Lightly grease a standard loaf pan with nonstick spray or butter. For easier removal, line the pan with parchment paper.

Prepare the wet mixture: In a large mixing bowl, combine the granulated sugar, eggs, sour cream, canola oil, lemon zest, lemon juice, and vanilla extract. Whisk until the mixture is smooth and fully blended.

Combine dry ingredients: In a separate medium-sized bowl, sift together the flour, baking powder, and salt.

Incorporate the dry into the wet: Gradually add the dry ingredients into the wet mixture, stirring gently until the batter is fully combined. Avoid overmixing to maintain a light texture.

Prepare the cream cheese filling: In a small bowl, mix the softened cream cheese and powdered sugar until smooth and creamy.

Layer the batter and swirl: Pour half of the batter into the prepared loaf pan. Add half of the cream cheese mixture on top and gently swirl using a knife or skewer. Repeat with the remaining batter and cream cheese, swirling once more to create a marbled appearance.

Bake the bread: Place the loaf in the oven and bake for 65 to 70 minutes. To prevent over-browning, loosely cover the loaf with foil during the last 20 to 30 minutes of baking. The bread is done when a toothpick inserted into the center comes out clean (excluding cream cheese spots).

Cool before serving: Allow the loaf to cool completely in the pan before slicing. This ensures the cream cheese swirl sets properly and the slices hold their shape.