Preheat oven to 450 degrees F. Slice the potatoes into large matchsticks and lightly spray them with canola oil. Season with salt and pepper. Arrange potato slices on a wire rack and place rack on a half-sheet pan. Bake until golden brown, about 30 minutes. When fries are almost finished baking, make cheese sauce. Serve fries with cheese sauce for dipping.
Dice cheese into equal-size cubes. Pour salsa into a microwave-safe bowl and add diced cubes. Microwave, covered, on high power for 2 minutes. Remove and stir. Microwave an additional minute if cheese is not fully melted.