For this game since it is 2 dimensional you will not be able to use the joysticks. It is easiest to use the d-pad. The L button will get you left and the R and Z buttons would get you right. You can technically use the A or X button to get you right and the B and Y buttons to get you left. The preferred control is the d-pad though. If you want to use GameCube controls for your project you can use the ones I coded in this project (just give me credit for them): https://scratch.mit.edu/projects/1147488286/
Credit to Nintendo for the original Controlls