If you are a Canadian resident who is not a U.S. citizen or green-card holder, you will be charged the U.S. 30% non-resident withholding tax when you have a gambling winning over USD 1,200 from eligible gaming in U.S. casinos.
However, because of the treaty signed between the United States and Canada, you can offset your gambling losses against your winnings up to the amount of your U.S. gambling winning for the year. You may be able to get all or at least some of the 30% tax withheld from casino winnings. To claim a refund of the U.S. taxes withheld from gambling winnings, you must file Form 1040NR, U.S. Non-resident Alien Income Tax Return. To file Form 1040NR, the following documents are required:
U.S. Form 1042-S issued by the U.S. casino which shows the U.S. withholding tax amount on your U.S. gambling winnings
Certified copy of a valid and current Canadian passport if you don’t have a valid U.S. Individual Tax Identification Number (“I.T.I.N.”)
Proof or evidence of your gambling losses such as gambling loss statement from the U.S. casino
If the U.S. casino does not provide you with your gambling loss statement, you should note all of your gambling activity (date, location of your U.S. casino gambling, what games you have played, and the amount you have won and lost) while gambling in the U.S. You should also keep appropriate documents such as ATM receipts or credit card statement showing the money you spent in the U.S. casino. Winnings from blackjack, baccarat, craps, roulette, and Big 6 wheel are exempt from the U.S. withholding tax. Thus, you cannot deduct your gambling losses from winnings on these games.You can only go back 3 years to claim a U.S. casino winning tax refund.