Got a title for the OP.
"STRIKE WITCHES 2 ~Egao no Mahou~" (笑顔の魔法;
Magical Smile), sung by Yoko Ishida, same as the first season. The OP single will include the song, an acoustic version and, if one orders the super limited edition, a DVD with live versions of the past two themes.
Edit: The ED has been confirmed as "Over Sky", with the first version being sung by Yoshika and Mio (the new Mio, that is.)
Three promos are available, one with the OP, one with the ED.