As the world becomes more integrated, the potential for estates to overlap jurisdictions increases. People can have multiple citizenships, homes in more than one country, investments connected to more than one tax jurisdiction and business interests that span borders. Further the laws that impact estate administration may not be the same in all relevant jurisdictions for a person. Therefore, to ensure the best results and avoid the potential for delays and conflict, it is important to take a global view to estate planning.
Examples of what can trigger tax filing requirements in the US are vacation homes located in the US, holding US securities personally, and being a US citizen. There is a tax treaty between the US and Canada to try to help reduce double taxation but careful planning is still required.
Some European countries have what is called "forced heirship" rules. These rules limit a person's ability to dispose of their estate the way they want and may have application even if a person no longer regularly lives in that country.
To ensure all aspects of estates that cross several jurisdictions are coordinated, it is important to have advisors with knowledge of the applicable laws in each jurisdiction. It may also be helpful to have professional advice from other advisors in those jurisdictions such as accountants and financial planners.