In OZ, you require an approval to use a photographers harness in lieu of the otherwise required seat belts. The details and conditions under which such a harness can be used are then put in your companies ops specs. This includes clear stipulations as to when the harness or seat belts have to be worn, as well as specifications for the harness to be used. For example, it must have an emergency quick release, the tether has to be the right length, it has to be attached to an appropriately rated hard point in the aircraft etc.
All good things to think about either way.
Since one is also required to wear a seatbelt in Canada, I would assume that a similar approval process would be required, although that is just a guess.
We had a purpose built helicopter harness when I was working down under. It had an emergency release similar to a parachute, and an adjustable length tether. I forgot the brand name, but I remember that it wasn't all that expensive.