Add charcoal and two handfuls of applewood chips to smoker. Light according to manufacturer recommendations. Bring to smoking temp (between 200-275).
Remove giblets and innards from the chicken cavity.
Pat the chicken dry with paper towels.
Mix spice rub and rub all over outside of bird.
Pour out or drink 1/4 of the Dr Pepper in the can. Add smashed garlic and fresh rosemary to the inside of the can. Place can in the can rack for the chicken. Carefully place chicken (drumsticks end down) over the rack so the can is in the cavity and the chicken is standing securely vertically.
Carefully place the chicken (still on can rack) vertically on smoker. Cover. Cook for about 2 hours, or until chicken hits 170 degrees F.
Notes
DO NOT USE quick light or match light charcoal for smoking. The long cook time and smoke will make your chicken taste like lighter fluid. Be patient in lighting the charcoal. Use newspaper if necessary to light the charcoal.Try not to check and uncover the chicken until close to the end of the cooking time, or you'll lose heat in the smoker and it will take longer and potentially dry out.