However, when you use a dual monitor setup, it is quite difficult to use a single wallpaper on both of the ... and choose Set for desktop > Desktop 1/2/3 or any other number that you may have.

Most wallpaper sites have some multi-monitor options, but there are a few places that specialize in super wide wallpapers, including Dual Monitor Backgrounds, WallpaperFusion, and subreddits like ...