Which car stereo will work on mine?

You may not be able to find a radio that your trucks wiring harness will plug right in to unless to go to Freightliner, which I wouldn’t do. You can take your radio out and take It to Best Buy’s installation dept(if they are open) and they can sell you the plug that will plug in to your trucks harness which I have done. Then you can connect the plug that comes with the new stereo to the plug you buy from Best Buy. The stereo in your truck usually will pull right out with a small screw driver prying the top and bottom.

 

While not specifically stating it is for a '14 Cascadia, This one matches what I remember a Cascadia plug looks like. Then you can get any single DIN stereo you want.
Metra® - Aftermarket Radio Wiring Harness with OEM Plug

 

Looks like about any Pioneer or Sony should fit right in there. You can always solder the right plug on, can get about everything you'd need at your local Walmart.

 

Oh, you also don't "need" a harness, just the wire diagram. That harness is just so you don't have to cut the factory harness.

Found a better place (maybe) for the harness... FREIGHTLINER RADIO HARNESS
And this is weird, I'm actually having trouble finding a wiring diagram.

 

That is exactly why I wouldn’t go to Freightliner. The plug and stereo both won’t be much more than $100.

 

Get the harness and removal key for $30, go to Car Stereo: Stereos, Radios & Receivers and get a stereo from anywhere from $30 to $600 depending on features. Or like mentioned above, go to Wally World, Worst Buy, or any other big box that sells electronics. You can easily get a new radio and harness for less than $100. I'd suggest the $150-$200 range for a quality one though.

 

It has been a few years since I built an adapter for a Freightliner but I do remember it was for a VW. Don’t waste the money for the tool to pull it out, a small screw driver works for your truck. It also fit in a Mack.