The Steam version of the game supports widescreen resolutions but they can be changed only in-game (the config tool was not updated apparently) and on some configurations that may or may not work properly.
To make sure that it works, after downloading the game, close Steam and go to the Bottle Manager. Select the correct bottle, go to the Control Panel tab and select Wine Configuration. In the window that appears, go to the Graphics tab and check the Emulate a virtual desktop option. Enter a resolution like 1280x720. Click Apply and then OK to exit.
Start Steam again and then the game. Go to the video settings and find your native display resolution. They game will inform you that it will restart with the desired resolution. It may still not look properly but it's ok. Close the game and Steam and then repeat the steps above to disable the emulate desktop option.
Start Steam and try running the game again. It should start with the proper resolution now.