I have an old horse buggy and would like to know how much it is worth
and the best way to restore it.  The plate indicates either WM MCCANN
with the MC underlined or WM MCGANN with the MC underlined and also
Weston, WV.  All the originial parts are on the buggy? I have done a
few searches, can't find information.  Please help.  Thank you.

Maybe the folks in Mifflinburg, PA  ("Buggy Town") can help you:
http://www.buggymuseum.org/registry.htm

The mention of there once being 50 buggy makers in Mifflinburg, and
another site's   speaking of 30,000 when Henry Ford started up,
suggests that they were small, local business.  One family site
mentioned a couple of buggy factory fires, resulting in the ancestor's
moving on, so the "factories" were not always of long existence.

A quick search of Google on the names hit 1.5 million sites with
McGann and 14+ million with McCann

Have you contacted the Carriage Museum of America?
http://www.carriagemuseumlibrary.org/about.htm