Millions more Americans might qualify for dual Canadian citizenship under a recent change to Canada’s requirements that has led to a surge in applications from its southern neighbor. Since the new law took effect Dec. 15, immigration lawyers in the United States and Canada say they have been overwhelmed by clients seeking help submitting citizenship applications. For people like Zack Loud of Farmington, Minnesota, it was a surprise to learn that under a new law, Canada already considered him and his siblings citizens because their grandmother is Canadian.