A new law may make it easier for millions of Americans to claim Canadian citizenship. This has prompted many people to research their family ancestry to pursue dual citizenship.

Potentially millions of Americans suddenly have a much easier path to Canadian citizenship, prompting a rush of people to explore their ancestry and file paperwork seeking dual citizenship. 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. “My wife and I were already talking about potentially looking at jobs outside the country, but citizenship pushed....