Game supports widescreen resolution by default, but the screen is only stretched.

Hor + solution:

Replace groove.exe depending on aspect ratio - Emperors New Groove.7z (mirror link)

For automatic aspect ratio support, use Brandondorf9999's fix.

The following float addresses in the executable are these elements:

16D6B1 - Horizontal Aspect Lock

16D736 - FOV

They're all in default of 1.