I owned a 2005 GMC Canyon and I have a 2007 Chevy Colorado as a work truck.
I used the unused sunroof circuit on the 2007, but only as an ignition switched circuit to control a pair of Kenwood radios. Those 2 radios (one VHF and one 800MHz) are wired to the battery for their power. The commercial radios, however, usually have a separate ignition sense circuit that can be used to automatically turn the radios on and off. This would be different than using it as the primary power for a CB.
Unless things drastically changed between 2007 and 2012, the wire, either cream or light yellow colored, its taped off inside the "A" pillar on the drivers side. Pulling that trim off will expose the wire harness. About half way up you'll see the wire taped off. I tied into the circuit there and ran a wire to where the RF decks are mounted under the seat. I installed a 3 amp fuse in the slot, since these ignition sense circuit only draw a few hundred milliamps at most.
I think the factory sun roof had either a 15 or 20 amp fuse, you could find that in the owners manual.
Anyway, back to CB's.
This unused sun roof circuit would work for what you need, however I'm not entirely confident you wouldn't pick up some noise. Only way to know would be to try. Your CB only needs a few amps, so installing a 5 amp fuse would work fine.
If your CB has 3 wires for the power connection, it'll let you tie the black and red direct to the battery for clean power and use the orange lead for the ignition sense circuit. Not all CB's are set up this way, so it'll depend on what you have.
Wiring the power in these trucks isn't hard. I had a VHF in my 2005 and wired both + and - direct to the battery, as is pretty standard in the industry. I was getting some alternator whine on my TX audio and I was able to fix it by taking the - lead for the radio off the battery post and moving it to a screw on the firewall to pick up body ground.
As for grounding, different radio manufacturers do this differently. Many Motorola, Kenwood and Icom come with leads long enough and instructions to tie the power directly to the battery. Fuses come installed on these leads so the circuit is fused within a few inches of the battery. Motorola's usually come with just the + lead fused. Some of the Icom's I've used had fuses on both + and -. This is a pretty hot discussion item and people will claim that one way is "right" and one way is "wrong".
Some higher powered mobiles, like 100 watt VHF and UHF mobiles, will come with a long fused + lead and a short - lead intended to be attached to a body ground near the radio. Usually it's a good idea to follow what the manufacturer is saying.
My recommendation is to do what the manual says, and follow that up with a short ground lead from the radio chassis to the vehicle body. This shorter ground path can help bleed of some noise, while maintaining a good connection to the battery.
