Hi,
Unless your guy has a us$ account at his bank, cashing a regular money order will cost him anywhre from $5 to $7 cdn. An international one will cost him anywhere from nothing to $3 depending on the type of bank account he as (you should check with him).
Now making an international money order will cost you a few $, and on a 10. transaction, that a very high % of fee's. Cash between two pieces of cardboard or eavy weight paper (can't be seen thru the light) in a registered envelope (less costly) seems the better solution. US$ are easy to change here, every bank will take them without fees and give us the daily exchange rate.