Who is doing this though? Is there a pattern?
TBH this is the problem I've had with the approach to this question, both from the government and indigenous groups.
There doesn't appear to be a "who" or some kind of individual or group or anything like that. The best hypothesis seems to be that native women are at a kind of nexus of vulnerable groups - the are more represented among run-aways, drug and alcohol addiction, prostitution, poverty, problems with the law, compared to other Canadian women. Do these along account for the higher rate of disappearances - well, we don't know. I suspect they account for a lot, but not all, of it.
Then there is the problem of police forces investigating. There seem to be more reason to think police forces have tended to ignore these cases, although it's again the case that they are also known to be rather lax at times in pursuing missing persons belonging to those other groups.
There's a real climate though that those kinds of questions aren't appropriate. I find it kind of depressing really, it seems like another case where an identity politics approach ends up looking at the surface issues in a way that obscures the more basic questions, like why indigenous women are so represented in those groups. I'm told this is a regressive POV.