Mailing Instructions

Hi,

I live in Canada, my mailing address is in Canada, and I'm applying for a visitor visa in Seattle office.

This is what the mailing instructions say:
If your mailing address is in Canada:

Persons currently residing in Canada on a study or work permit who are applying for a new temporary resident visa must not submit a return a prepaid envelope.
The Consulate will send mail to addresses in Canada via U.S. Postal Service First Class Mail. Please enclose with your application a self-addressed return envelope.

So, to confirm, does it mean I have to enclose a return non-prepaid envelope?
Can we buy this in Canada Post?
What do we need to write in the return non-prepaid envelope? My address and CIC address or just my address?

Thanks