Disney has completed the casting of its coven for “Oz, the Great and Powerful,” tapping Michelle Williams to play Glinda, the good witch.Sam Raimi is set to begin helming the pic, which will lense in Michigan, in July. Williams will team with snake-oil salesman James Franco to face off against her evil sisters, to be played by Rachel Weisz and Mila Kunis, in a struggle for control of the magical land of Oz. Williams most recently appeared in “Blue Valentine,” opposite Ryan Gosling, and has wrapped “My Week With Marilyn” and “Take This Waltz,” the latter of which is making the rounds at Cannes. The prequel to “The Wizard of Oz” was penned by Mitchell Kapner and David Lindsay-Abaire. Joe Roth produces. No release date has been set, but Disney is eager to have “Oz” follow in the footsteps of “Alice in Wonderland,” which broke the $1 billion mark at the B.O. Pic could bow as early as fall 2012.