If your migration was based on an import script then topics (and probably posts) include an import_id custom field. You can then use those custom fields, Permalinks, and SiteSetting.permalink_normalizations to make redirects.
You can test in rails with something like
tcfs=TopicCustomField.where(name: 'import_id')
pcfs=PostCustomField.where(name: 'import_id')
If you don’t have those, then it’s going to be Really Hard.
If you do have those, then you can do something like
tcfs.each do |tcf|
Permalink.create(url: "imported-topic/#{tcf.value}", topic_id: tcf.topic_id)
end
And then make a PermalinkNormalization that redirects the path for topics to /imported-topic/IMPORTED_ID.
You can grep the import_scripts` to find some other import scripts that set Permalinks and the permalink normalization.