Scanner Radio and Scanner Radio Pro don't currently contain support for ChromeCast but you can still listen over Google Home and Chromecast devices by having the Google Home app send your phone's audio to them.
To do that, follow these steps:
- Install the Google Home app if you don't already have it installed, you can get it from https://play.google.com/store/apps/details?id=com.google.android.apps.chromecast.app
- Launch the Google Home app.
- Select the device you want to send the app's audio to.
- Tap on the "Cast my audio" button at the bottom of the screen.