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.
- Press the account button in the bottom-right corner of the screen (it looks like a person in a circle).
- Scroll down and select "Mirror device".
- Select the device you'd like to send the audio to.