Apparently there is no customs doodie when importing gold from Canada to the US, but what about silver?
Gold coins, medals, and bullion may be brought into the U.S. However, under regulations administered by the Office of Foreign Assets Control, such items originating in or brought from, Cuba, Iran, and Sudan* are prohibited entry.
Copies of gold coins are prohibited if not properly marked by the country of issuance. The importation of counterfeit coins is prohibited.
There is no duty on gold coins, medals or bullion but these items must be declared to a Customs and Border Protection (CBP) Officer. Please note a FinCEN 105 form must be completed at the time of entry for monetary instruments over $10,000. This includes currency, ie. gold coins, valued over $10,000. The FINCEN definition of currency: The coin and paper money of the United States or any other country that is (1) designated as legal tender and that (2) circulates and (3) is customarily accepted as a medium of exchange in the country of issuance.
If you have doubt whether your gold/gold coin is considered a monetary instrument it is in your best interest to declare the item(s) with a CBP Officer, so you do not give a false declaration.