Heart of Crown

When opponent plays a military card, such as an Infantry Battalion or Imperial Calvary, can I reveal a Magic Talisman and resolve its ability?

Yes. You can use any Defense card against any Attack card. When you reveal a Magic Talisman from your hand, since it goes on top of your draw pile, the number of cards you can use Magic Talismans to defend against is limited by the number you have in your hand.