Most US $ money orders are international which means they can be cashed almost anywhere. To date I have been able to cash American Express, Winn Dixie, Walmart and Western Union Money Orders without a problem. As banks may differ I recommend checking with your bank.

The only problem that may arise is with USPS (United States Postal Service) Money orders. The USPS issues 2 different types of money orders. The International one is Pink and can be cashed in Canada. The Domestic one is Green and only cashable in the US. If you accept money orders be sure to specify to your US clients not to send the Domestic ones.