Baseline (Widescreen) Solution & Issues
The game initially runs at 1280x720. Select any resolution from the main menu under Options, Graphics Options and hit Back to apply.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
If the picture is stretched, make sure 2560x1080 is selected in the game's display options then open your monitor's OSD menu.
In the display settings, you should see aspect ratio and by default it's set to Auto. Change that to 21:9 and that should correct the stretching issue. You should be able to go back in the monitor menu and set the option back to auto afterwards and the problem should go away.
Eyefinity / Surround Specific Solution & Issues
Patch 1.4 brought native/Hor+ support.
In ARs narrower than 48:9, gameplay is Hor+ AND letterboxed. In menus, horizontal mouse speed is greatly reduced. Gameplay is unaffected.
Some cut-scenes are seen through the combat drone's orange eye. The orange overlay scales incorrectly in multi-mon (1.73:1 design, pillarboxed to Surround, then squished to the central 16:9 portion). There's a TV stream on a billboard in Moscow that has the same flaw (beginning of mission Invisible Bear).
4k UHD Specific Solution & Issues