You can take a look at the source code of the following Flutter plugin: sirikit_media_intents. The plugin enables SiriKit Media Intents implementation into the Flutter app; obviously, media intents are not suited for the kind of voice interaction you need for your app, but the concept is basically the same for the other SiriKit intents domains (you may need to implement a custom intent).

There is just one technical aspect you should consider: your app must adhere to the in-app intent handling strategy (iOS 13+), in order to use Flutter Channel Methods, and that requires your app to enable multiple scenes support .