The requirements for pet imports to the United States are detailed per animal species on the website of the United States Department of Agriculture (Animal and Plant Health Inspection Service) USDA APHIS Pet travel. Different states can also have additional requirements. Note the conditions for a possible transit through another state!
You can send questions directly to the United States authority USDA from here. You can also find prepared answers on their pages using different search words (e.g. dog import).
You can also enquire about the conditions for export from the U.S. embassy in Helsinki.