Baseline (Widescreen) Solution & Issues
Native.
The game will run at your desktop resolution upon first launch. You can also set your resolution and aspect ratio in-game, and even force 16:9 anamorphism thanks to Options, Advanced, Letterboxing Aspect Ratio (if you prefer letterboxed 16:9 on a 16:10 display for instance).
Settings are saved in C:\Program Files\Steam\userdata\<random digits>\<more random digits>\local\SeriousSamHD.ini
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
Native support.
Gameplay: Hor+
HUD: scales correctly, can even be centered using Screen Width in the Graphics options
Cut-scenes: pillarboxed
5040x1050, Max 3D Rendering MPIX: Unlimited
Default/centered HUD & UI (using the Screen Width slider or the gfx_fSafeAreaX value)
4k UHD Specific Solution & Issues