parameters = {'INPUT': QgsProcessingFeatureSourceDefinition(layer1.id(), True),
              'OVERLAY': QgsProcessingFeatureSourceDefinition(layer2.id(), True),
              'OUTPUT': 'memory:'}
differenced = processing.run('qgis:difference', parameters)

QgsProject.instance().addMapLayer(layer1, False)
QgsProject.instance().addMapLayer(layer2, False)