If we're talking about being part of a foreign investigation because of an accident that happened on foreign soil but in which Canada has a direct interest, the body that sets those standards and recommended practices is the International Civil Aviation Organization.
If we use the parallel with the Iranian PS752 accident, where again Canada has only “expert” status, in accordance with ICAO annex 13, in that case the TSB has actually received more access to the site, the wreckage and the investigating agency—even though it's being led by Iran—than we're entitled to as experts, even in the same situation.
It would really be up to ICAO to make the changes so that when a country like Canada, or another state, has a significant number of fatalities, as well as recognized expertise to contribute, we should be able to play a more active role in the investigation.