I'm thinking that anything that's ever held gas in it MUST be shipped with ground transport only.
Actually, after checking the Canada Post website I found this:
Canada Post will not otherwise accept packages that contain dangerous goods or that display dangerous goods symbols. Canada Post must assume that all markings and labels on a package identify the actual contents. If any evidence of former hazardous material contents is visible on the box, the parcel cannot be accepted.
Direct link HERE
Also, read everything under Section 6.
I believe the only way to properly ship these items is by being properly labelled, though courier ground transport ONLY.