Can we use sound clips under fair use on Wikipedia while maintaining that the encyclopedia is covered by the GFDL?
The GFDL applies to our original content. If someone wants to use an article from here (or an original image or sound clip), he is free to do so if he abides by the GFDL. WE are free to include some sounds and images that are fully copyrighted under fair use; someone else who gets them from our site will still himself have to qualify for fair use--the GFDL does not apply to works we have included here under that doctrine. That's why it's important do document the source of an image on its description page--just because WE have the right to use it doesn't mean that everyone using Wikipedia articles also has that right (though many probably will).
What about songs that are under, say, Canadian copyright? Canadian copyright law has no provisions for "fair use".
If Canada wants to extradite, let them try.