There's an audio subforum on the site.
I'll give you the quick version, but you'll want to browse the subforum.
The interface / harness products I like are from Axxess / Metra. Others here like PAC. I'd stay away from Scosche, myself.
First -- the stock system is 'Bose'... 'Boss' is an aftermarket car audio company, but you're replacing 'stock', so that has to be Bose. Just so we're on the same page...
You want GPS / BT / backup cam. You probably also want to retain your chimes (they're built into the radio), and you want SWC retained. You also want to retain the amp that's built into the factory system (although they're known to break, given enough time).
You'll need:
- Radio interface harness (either one that retains the amp, or one that lets you add your own amp)
- To retain Bose amp (and OnStar, if you use it): GMOS-04
- To build new system with either no amp or a replacement amp: Metra LC-GMRC-01
Both of these come with the external 'chime box' (which provide door chimes, driver info center (DIC) audio notifications, etc., etc.). They'll also preserve RAP (retained accessory power, which keeps the radio on for 5min at key-off, or unless you open a door, sooner.)
Also note that Metra is revamping their harnesses -- you can still get the above at Amazon, but you won't find these listed at their own website. These are the cheapest options; their 'new' ones are more 'universal', but that universal compatibility comes at a higher price point.
By using a harness, you'll preserve the vehicle's CANBus (the OEM radio is on it), and save yourself a LOT of headache figuring out the wiring connections. The harnesses contain the corresponding interface plugs that connect right up to the GM harnesses -- no wire cutting. You wire your aftermarket radio harness to the adapter harness, and plug right into the GM harnesses after you remove the radio (oh, and you'll need to cut out a piece of plastic from the back of the dash to fit the new radio in; no biggie).
- The radio / head unit
You have many choices here, at many price points. Depending on what smartphone OS you use (Android, Apple), you can get a unit that will leverage that OS' mapping apps (and save $$$, vs. actually having GPS built-in, which also needs to be updated from time to time, etc., etc.)
Since you want GPS, you'll want a double-DIN size radio (and a cheap installation kit to go with it, along with an antenna adapter (GM uses a proprietary sized plug that doesn't fit standard inputs).
To use the smartphone with the radio for maps, you'll want something with a USB interface built-in. Front is more convenient, but most double-DIN / touchscreen units have rear inputs, so they can maximize the display screen size. Adapters are available to run cabling to an outboard USB input (recycle one of the 12v power plug receptacles to mount it)
- Steering wheel controls (SWC):
I like the Axxess ASWC-1. It integrates nicely with the GMOS-04, easy to program.
Same applies as with the radio interface harnesses, as far as availability, etc.
- Backup camera: Again, lots of choices / price points. You'll need to wire it to your reverse lamp circuit, so it turns on automatically. You can also wire them to switched +12V (which will allow you to turn the camera on at any time -- but you'll need to activate it manually for 'reverse' gear).
Those items above will allow the most plug-n-play, allowing you to re-use your factory amp / speakers.
If you want to go farther than that...
To replace the speakers in the front doors requires adapter mounts, as GM / Bose used 8" mid-bass drivers in the front doors. You also have tweeters in the upper / front dash. The factory amp provides the crossover duties.
The factory amp is behind the rear passenger side panel, unless you have a long wheelbase (EXT, XL); then it's on the driver's side.