Stop to consider that perhaps he is flying pipeline patrol
to ensure YOUR safety. Maybe he is a volunteer flying needed
blood, or organs for transplant. Could be law enforcement on traffic watch. could be a guy making his living taking photos of aerial views of property, .May be there is a private grass strip that the public(you) are not aware of, and he is going there,,,,could be many things Flying low is not endangering you any more than a airliner at 30,000'
Your statement by the time we hear him coming its too late to get a good look tells me he is not overhead long, so noise should not be an issue, have a dog barking nearby? he is louder than a C172 at 500 feet, and barks for a lot longer.why are you upset? He also could have a low altitude waiver, if not the following might apply .
To address your question on what is legal in CANADA ,( the above regards the FAA's rules for the US)
Permissible Low Altitude Flight
602.15 (1) A person may operate an aircraft at altitudes and distances less than those specified in subsection 602.14(2) where the aircraft is operated at altitudes and distances that are no less than necessary for the purposes of the operation in which the aircraft is engaged, the aircraft is operated without creating a hazard to persons or property on the surface and the aircraft is operated
(a) for the purpose of a police operation that is conducted in the service of a police authority;
(b) for the purpose of saving human life;
(c) for fire-fighting or air ambulance operations;
(d) for the purpose of the administration of the Fisheries Act or the Coastal Fisheries Protection Act;
(e) for the purpose of the administration of the national or provincial parks; or
(f) for the purpose of flight inspection.
(2) A person may operate an aircraft, to the extent necessary for the purpose of the operation in which the aircraft is engaged, at altitudes and distances less than those set out in
(a) paragraph 602.14(2)(a), where operation of the aircraft is authorized under Subpart 3 or section 702.22; or
(b) paragraph 602.14(2)(b), where the aircraft is operated without creating a hazard to persons or property on the surface and the aircraft is operated for the purpose of
(i) aerial application or aerial inspection,
(ii) aerial photography conducted by the holder of an air operator certificate,
(iii) helicopter external load operations, or
(iv) flight training conducted by or under the supervision of a qualified flight instructor.
Minimum Altitudes and Distances
602.14 (1) [Repealed]
(amended 2003/03/01; previous version)
(2) Except where conducting a take-off, approach or landing or where permitted under section 602.15, no person shall operate an aircraft
(a) over a built-up area or over an open-air assembly of persons unless the aircraft is operated at an altitude from which, in the event of an emergency necessitating an immediate landing, it would be possible to land the aircraft without creating a hazard to persons or property on the surface, and, in any case, at an altitude that is not lower than
(i) for aeroplanes, 1,000 feet above the highest obstacle located within a horizontal distance of 2,000 feet from the aeroplane,
(ii) for balloons, 500 feet above the highest obstacle located within a horizontal distance of 500 feet from the balloon, or
(iii) for an aircraft other than an aeroplane or a balloon, 1,000 feet above the highest obstacle located within a horizontal distance of 500 feet from the aircraft; and
(b) in circumstances other than those referred to in paragraph (a), at a distance less than 500 feet from any person, vessel, vehicle or structure.