(Tengo esta misma guía escrita en español acá)

Call of Juarez: Gunslinger is one hell of a singleplayer first person shooter, so i'll help you get the most out of it.
Sadly, the ingame options are really limited so we're gonna have to edit the configuration file located outside of the game's root folder. I'm gonna show you step by step how to edit that file so you can get rid of the black borders and change some other interesting things.

Before we start i want to clarify that this is my first guide and that english is NOT my main language, so bear with me please. Also, be advised that this guide is for Windows, i don't know how much the steps could differ other than clicking on a different option when downloading Notepad++, but yeah.

(EDIT: Kostr184 mentioned that Notepad++ is NOT NEEDED for this, you can just rename the file from "Video.scr" to "Video.txt", open it with the regular notepad and then change it again to "Video.scr". So you can skip this step if you desire.)

First off we've got to download Notepad++ since the config file is in .scr format and can't be opened with the regular notepad.

Head off to the download page[notepad-plus-plus.org] and click on the lastest version. There are mainly two options that you can choose;
If you have a 32-bit operating system, then the first option (32-bit / x86) is the adecuate option, click on • Installer down in the Download 32-bit x86 section.
If you have a 64-bit operating system, then the second option (64-bit / x64) is what you should choose, click on • Installer down in the Download 64-bit x64 section.

Then install it, and now we can start editing the config file.

The config is located in: C:\Users\yourusername\AppData\Local\techland\cojgunslinger\out\Settings.
If you don't know what's your Windows username then head to C:\Users.
The config file we're gonna edit is Video.scr.

Right click the file and choose Edit with Notepad++.

Now straight to the reason you're probably here.
• To remove the black, painted borders you just need to add this line at the bottom and end of the file:
DisableScreenBorder()
Then you'll be left with two, almost equally annoying black bars, commonly known as a letterbox.
• To remove the letterbox / make the game truly fullscreen, you just need to add this line at the bottom and end of the file:
RenderViewportProportion(-1, -1)

• To change the console-like FOV you just need to add this line at the bottom and end of the file:
ForcedHorzFov(preferredFOV)
You can enter values between 80 and 110. Personally i recommend to use 100.
The default FOV is 82.72.

• To enable the Anti-aliasing setting you need to:
Search the line FSAA(0) and change it to FSAA(1).

• To change the Anisotropic setting you need to:
Search the line Filtering(Anisotropic) and change the value (Anisotropic) by the one you desire: (From left to right increasingly GPU intensive) Bilinear, Trilinear, Anisotropic, AnisotropicTrilinear.
(The value you get by default on the file could be totally different, but the process is still the same)

• To change the resolution to your heart's content you just need to:
Search the line Resolution(1360,768) and change the value (1360,768) to the one you desire.
(The value you get by default on the file could be totally different, but the process is still the same)

I'll leave here how my file ended up looking so you can check if you don't know where you should add the new lines or how it "should" look.

Now you're ready to enjoy Call of Juarez: Gunslinger at it's fullest!
Feel free to correct me, to give your opinion and to edit, experiment & try out things with the config file, just make sure to have a back-up.

Have fun!