Thanks for the feedback Colludium and jayderyu!
You guys are probably right that it's a bad idea. I'll probably have to bite the bullet and incorporate the mouse as well, which should work but I just wanted to have more traditional platformer controls.
Gamepad controls are currently:
Analog/d-pad - Cannon rotation/movement
X - Shoot/Action (hold for charged shot)
A - Jump
Y - Enter/Exit vehicle
B - Shield (also pulls in item drops)
Left trigger - Speed boost powerup
Right trigger - Brake
Left shoulder - Weapon select (multiple selections)
Right shoulder - Weapon cancel
Start - Pause/map
What I can do is have have cannon rotation and shooting mapped to the mouse, and the movement mapped to the keyboard; more like an FPS. It would play quite different compared to the gamepad, but I may just have to suck it up and do it anyway.