The double din in this 2006 Buick Lucerne CXS is a Pioneer AVH-X3800BHS. Highlighted features are bluetooth, USB input, auxiliary input, and the ability to add a SIRIUSXM tuner. The radio also has a backup camera input should you choose to add one.
In order to mount the radio we used a 95-3305 double din dash kit. As you can see in the picture the kit fits nicely. It shouldrun you around $25.
We also needed to retain the data from the vehicle's on board diagnostic computer, so we used a C2R-GM29 data retention harness. GM started running vehicle data through the radio back in about 2002. So vehicles after that point in time need a data harness to be able to keep the data communication between the vehicles diagnostic computer and the rest of the electronics in the car.
If you don't use the correct harness for this vehicle, you will have issues down the road. You will pay around $100 for the wiring harness. If the harness you are looking at buying is $20 or less, you are buying the wrong one.
And as in any other late model GM vehicle we needed an antenna adapter to retain AM/FM radio signal, which is a 40-GM10. The factory antenna will not plug into the stereo without this adapter. They cost about $15 at a retail store.
Once you have all these parts together you should be ready to install a double din into this vehicle. You will just have to decide what stereo you want to have in the car.