Handling iOS and Android Notification Payloads in Flutter using Firebase

I want to be able to handle iOS and Android notifications using Firebase Messaging.

I followed a tutorial in which the person received notification payloads in this format on Android:

notification:{ title: "title" , body: "body" } }

However on iOS I am receiving a payload in this format:

aps:{ alert:{ title: "title" , body: "body" } }

What is the best way to handle this within Flutter when configuring firebase messaging like below?

_firebaseMessaging.configure(
  onMessage: (Map<String, dynamic> message) async {
     showDialog(
      context: context,
      builder: (context) => AlertDialog(
        content: ListTile(
          title: Text(message['aps']['alert']['title']),
          subtitle: Text(message['aps']['alert']['body']),
        ),
        actions: <Widget>[
         FlatButton(
            child: Text("Dismiss"),
            onPressed: () => Navigator.of(context).pop(),
          )
        ],
      ),
    );
  },

Are these payloads customizable or should I be doing something like:

if (Platform.isIOS) {
...Text(message['aps']['alert']['title']),
} else {
...Text(message['notification']['title']),
}