The IRS requires wins of $1200 and above to be reported. This means you don’t need to worry about taxes if you win an amount less than that, but if you do, the casino will issue you a W-2G form. Here, you will provide your name, address, and Social Security Number. If the amount you won is less than $5000, the casino will not deduct withholding tax as long as you give them your SSN. However, if you refuse to disclose your SSN, the casino will withhold 28% of your winnings.
There are slightly different taxation rules for foreigners though. The IRS defines a foreign person as a non-resident alien, so tourists fall under this category. Upon getting a taxable win, 30% of the amount will be withheld. However, if you are from one of the treaty countries included in the IRS Publication 515, you can get a refund of the taxes withheld. Canada is one of the treaty countries listed in the publication.
Another common issue is whether or not gamblers will be taxed if they are playing on American Indian land. The answer is yes, the same rules apply to winnings you get from casinos on these lands.