Personal Allowances and Exemptions for U.S. Citizens or Residents
Under 48 hours
After a stay of less than 48 hours in Canada, a US citizen or resident may return to the US with:
USA US $200.00 worth of goods per person, tax and duty free
USA Any purchases of alcohol or tobacco products may be subject to duties and taxes (A)
USA Any purchases in excess of the US $200.00 allowance may be subject to duties and taxes

Over 48 hours
After a stay of 48 hours or more in Canada, a US citizen or resident may return to the US with:
USA US $800.00 worth of goods per person, tax and duty free
USA Purchases may include 1 litre of alcohol (must be 21 years of age or older), 200 cigarettes (1 carton), and 100 cigars, tax and duty free (must be 19 years of age or older)
USA Family members may combine their tax and duty free allowances
USA Any purchases in excess of the US $800.00 allowance may be subject to duties and taxes (A)

Rates
(A) DUTY AND TAX RATES ENTERING THE US
IF YOU EXCEED your duty free allowances and exemptions entering the US, the following approximate US duty and tax rates apply:
USA USD $2.00 - $3.00 per bottle of liquor*
USA USD $1.90 per case of beer*
USA USD $10.07 per carton of cigarettes
  * US duty rates on purchases exceeding 1 litre of alcohol are assessed according to alcohol content.