You don't want to purchase the international reply coupons in Canada. They are a horrendous price that will give you only a single first class stamp back to Canada. That is why hams never cash them but just keep reselling them or exchanging them ('')

What I have done is purchase US stamps on a trip down there so that I have a stock of them, or to send a money order to some kind sole who will purchase stamps for me, use what is needed for the swap and send the rest back to me to use for other swaps. Many people do not mind doing a favour like that.

Until I was able to get no cost money orders from the bank I never worried about sending a few dollar bills in an envelope (just make sure that they are not visible). I have never lost any, but if I did I figure what I have saved on the cost of money orders would cover the occasional loss.

Good luck.