Baseline (Widescreen) Solution & Issues
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
The Game only Supports 4:3,16:10 and 16:9 resolutions.
I created a Resolution and Aspect Ratio Fix via CheatEngine.
Start the Game and go to the Video Options Menu, Alt Tab and start the Mercenaries2-Origin.CT.
Now fill out your 2xWidth, 2xHeight and 2xAspect - see Additional Screenshot 3440x1440 FIX.
Go back to the Game and you have 21:9 with a higher FOV.
Eyefinity / Surround Specific Solution & Issues
Same as in Ultra-Widescreen but unfortunately the FOV become way to big - see Additional Screenshot.
4k UHD Specific Solution & Issues