I'm going to say a few things about the postal system that may be too controversial to stand, but I base everything I say on personal experience.
There is definite hypocrisy in the way Canada Post treats cash. Notes are considered documents, so they cannot be insured. However, for the purposes of sending them outside of the country, notes are also considered commercial goods and must be declared. But why would anyone want to declare cash when the package can't be insured? It's a definite catch-22 that is absolutely designed to help CP avoid paying for lost items.
I've never had a registered letter to the U.S. fail to reach its destination, but some have been delivered without being tracked. The problem is that the United States Post Office (USPS) treats international registered letters like regular mail. They make no money from accepting and delivering these letters, so they have no incentive to keep the tracking updated. If anything, registration just alerts postal employees to the potential of something valuable being inside. Consequently, I have stopped offering registered mail as a shipping option to the U.S. Service standards for Xpresspost to the U.S. have improved, and not coincidently, Xpresspost is much more expensive now than it was three years ago, but it's definitely safer IMHO. I have not had any problems with Xpresspost to the U.S. in recent times. U.S. postal employees seem to respect the Xpresspost service standards.