qgis 3 - How to turn on the 'on-the-fly' functionality with PyQGIS?

Before QgsMapRenderer was deprecated if we wanted to activate OTF we used code like this:

canvas = QgsMapCanvas()
canvas.mapRenderer().setProjectionsEnabled(True)

Currently, QgsMapRenderer is divided into two classes QgsMapSettings and QgsMapRendererJob. I did some research, but with no success. So how we can achieve the same now?

Answer

Not sure if this will be possible as according to one of the QGIS devs @ndawson in response to Feature request #11644:

"Disabling on the fly projection is no longer an option in QGIS 3.0"