Depends, an Italian Magazine said one spell at a time, but GameInformer said two spells, one for each hand. --- And the Lord said unto John, "Come forth and receive eternal life." But John came fifth and won a toaster.
I think I will go with gameinformer. Also there have been a lot more that says you can use spells in both hands. Everything that is 1 handed can be used in both hands including shields --- If you want Megaman X and MMZ Zero in Marvel VS Capcom 3 Put this message in your signature.