Wii widescreen doesn't appear to work

Solution 1:

You have to use the proper output cable to get 480p. If memory serves, you need to use component output. Out of the box, the Wii comes with a composite output cable. You'll need to purchase a separate Wii component output cable.

From Nintendo's product page:

The Wii Component Video Cable allows you to hook your Wii console system to a high-definition TV (HDTV) or enhanced-definition TV (EDTV) to view 480p progressive output. 480p progressive output displays at a higher resolution than standard 480i resolution....

Please note that your TV must be a high-definition TV (HDTV) or enhanced-definition TV (EDTV) to view 480p output. You will also be required to change your Wii settings from Standard TV (480i) to EDTV/HDTV to view 480p....

You cannot see Wii progressive display output when the Wii console system is hooked to a TV using any other kind of cable.

Solution 2:

The Wii uses analog video signals. To my knowledge, analog signals do not carry information about whether the signal is standard definition or widescreen.

This means you have to change the settings on your TV for that channel to widescreen.

As for the cable, Widescreen may only work with component cables as splattered bits already mentioned. Even if it isn't, the system will not support progressive scan mode without it.