Set up grill for direct cooking and heat to medium. Once hot, clean and lightly oil grates with canola oil. Whisk together lime zest and juice, olive oil, and maple syrup in a bowl; transfer half to a small bowl and reserve for basting. Add chicken and sweet potatoes to remaining marinade and toss to coat; let stand 5 minutes.  Thread chicken and sweet potatoes onto skewers; discard marinade. Season chicken with salt and pepper. Grill, covered, turning occasionally, and brushing twice with marinade, until chicken is cooked through, 10 to 15 minutes.