How do Canadian handle return postage or do you swap.

I'm on a border city and close to the ferry. I can do a pre-paid envelope to the ferry and pay $5 to pick up there. I also have been shipping from the US to for the swaps because I can ship to the person, pre-pay a return envelope and pick up the package at the ferry for cheaper then it would cost me to just ship the swap! Many I know are ok with me sending a US money order but to ship to canada sometimes is crazy!

Did you know that the Canadian postal service will use a US international stamp but the US postal service won't with a Canadian stamp? I learned that when I was mailing out wedding invitations.