Incidentally, Ammurican (and other) visitors to Canada are able to
reclaim their GST/HST payments, though whether the effort to track a
few pennies on postage would make sense... (!)

Not any more. The GST rebates ended in April 2007. Now there's a limited
rebate for tours and an arcane set of special cases for things like works
of art produced for export.

R's,
John