Baseline (Widescreen) Solution & Issues
Hor+ via a hack.
Just download the hack attached below and un-zip into your Just Cause folder ... where the JustCause.exe is located
Now open up the resolution.ini file and change the resolution to the one you desire ...
Start the game it should run in the chosen resolution ...
Through the hack the game is Hor+, however the HUD stretches.
The menu stretches also.
The Map and PDA screens (as well as the PDA sub-menus) stretch.
The pre-rendered cut-scenes (including the opening videos) stretch, however all of the in-game cut-scenes minus the intro are Hor+.
Download available from the PC Gaming Wiki Community Files (search there).
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
4k UHD Specific Solution & Issues