The flight plan helps Customs distinguish between legitimate flights,
and those
attempting to illegally smuggle French Canadians south across the boarder.

Canada has for many years now been engaged in a covert campaign to export
their "French Problem" south to the US. Thru false bottom trucks, small
boats
across the rivers, and aircraft under radar, Canada is attempting to
remove the
French Canadians and smuggle them into the French speaking neighborhoods of
Louisiana, NYC and Washington.

The US had originally intended to send the illegal French Canadian
Ouetbacks to
Guantanimo. But those plans had been canceled when Al-Queida prisoners
said they
would rather have electrical wires attached to their genitals than share
a cell with the
French.

Robert M. Gary wrote:

Does anyone know the actual reason you're required to file a flight
plan when crossing the boarding between the U.S. and Canada? Does
someone sit down at the end of the year and try to count operations
based on them? They carry NO customs benefit since customs are handled
separately.

Usually, when we fly south into Mexico, we don't both filing since the
U.S. has no way to actually hand the flight plan to Mexico. Most of
the Mexico AOI don't even have working phones, much less computers.
However, they are always happy to see you arrive at any time. Of
course crossing the ADIZ northbound from Mexico is a different thing
all together.

-Robert