Gilead only dissolved the legality of the adoption within their own borders, though. Their retroactive change in laws does not invalidate the decisions made by other countries on behalf of THOSE countries - that's not how any of this works (believe me when I say I have spent a LOT of time studying the ins & outs of immigration the last few years where it involves the relationship allowing for immigration being illegal in one of the two home countries).

The paperwork lodged for Oliver to obtain his citizenship in Canada must meet Canadian laws and requirements - the fact that the relationship which is allowing for citizenship (in this case as an adopted child) is illegal in another country has zero bearing on it - it is legal in Canada. Their marriage is still legal and valid in Canada.

Once again - Gilead cannot revoke his Canadian citizenship on behalf of Canada without the Canadian authorities saying "yeah, OK guys, you don't like this thing so we're going to agree that's a thing that we no longer allow as a legal basis for immigration/citizenship ... but only from your country"

The problem you have listed as an example is ... not at all like this. That is a case of improperly filed paperwork in one country (presumably the USA - if it was not done correctly in Haiti it would be safe to assume that the child wouldn't have been allowed to leave the country) meaning that the child has no legal status (in which case she should absolutely not be removed from the country because she wouldn't be let back in, which don't get me started on how ridiculous THAT point is if she's a child) - as opposed to a child being a legal dual national by adoption/descent/birth where his status in one of those countries is now in question because of the change in laws in that particular country.

As an aside I hope they have found a better lawyer and are on the way to getting it all sorted out. Immigration is a pain and adoption and immigration at the same time is the absolute worst.