We are developing a custom Lightning component that contains a Canvas App which loads our external site inside of the Lightning component.

Is it possible, and if so what are some recommended ways to communicate between the Lightning component and the loaded Canvas App site? (NOT the parameters passed in to load the canvas app initially.)

For instance, we would like a button in the Lightning component to trigger an action inside the loaded Canvas App.

It seems that various methods of communicating are restricted by Lightning Locker etc.  I found documentation for various methods of event raising and handling but all I've tried have been without success.  It seems possible they're only for communicating from Lightning component to Lightning component, or from canvas app to canvas app (or Visualforce), but not Lightning component to canvas app.
https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/events_component.htm
https://developer.salesforce.com/docs/atlas.en-us.platform_connect.meta/platform_connect/canvas_app_events.htm

I was able to send a message from the canvas app to the lightning component using this "non-standard, probably unsupported technique", but not the other way around.
https://salesforce.stackexchange.com/a/161621/49367

We are developing a custom Lightning component that contains a Canvas App which loads our external site inside of the Lightning component.

Is it possible, and if so what are some recommended ways to communicate between the Lightning component and the loaded Canvas App site? (NOT the parameters passed in to load the canvas app initially.)

For instance, we would like a button in the Lightning component to trigger an action inside the loaded Canvas App.

It seems that various methods of communicating are restricted by Lightning Locker etc.  I found documentation for various methods of event raising and handling but all I've tried have been without success.  It seems possible they're only for communicating from Lightning component to Lightning component, or from canvas app to canvas app (or Visualforce), but not Lightning component to canvas app.
https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/events_component.htm
https://developer.salesforce.com/docs/atlas.en-us.platform_connect.meta/platform_connect/canvas_app_events.htm

I was able to send a message from the canvas app to the lightning component using this "non-standard, probably unsupported technique", but not the other way around.
https://salesforce.stackexchange.com/a/161621/49367

We are developing a custom Lightning component that contains a Canvas App which loads our external site inside of the Lightning component.

Is it possible, and if so what are some recommended ways to communicate between the Lightning component and the loaded Canvas App site? (NOT the parameters passed in to load the canvas app initially.)

For instance, we would like a button in the Lightning component to trigger an action inside the loaded Canvas App.

It seems that various methods of communicating are restricted by Lightning Locker etc.  I found documentation for various methods of event raising and handling but all I've tried have been without success.  It seems possible they're only for communicating from Lightning component to Lightning component, or from canvas app to canvas app (or Visualforce), but not Lightning component to canvas app.
https://developer.salesforce.com/docs/atlas.en-us.lightning.meta/lightning/events_component.htm
https://developer.salesforce.com/docs/atlas.en-us.platform_connect.meta/platform_connect/canvas_app_events.htm

I was able to send a message from the canvas app to the lightning component using this "non-standard, probably unsupported technique", but not the other way around.
https://salesforce.stackexchange.com/a/161621/49367