In the past 3 months we have been using the USA AIRMAIL standard size prepaid box and had no problems shipping so far to those over seas that insist they try the products.
We have not tried Canada, who have a past record of stopping our boxes or at the very least putting a big import tax. If you want to take the chance, we can try 1 box and I suggest capsules and not liquids to first see if they have any problems.