In case gesturePolicy is DragThreshold and the threshold is exceeded:

It does not take an exclusive grab, so when you drag past the drag threshold, it does not receive QQuickPointerHandler::onGrabChanged(CancelGrabExclusive), and does not receive QQuickPointerHandler::onGrabChanged(CancelGrabPassive) either. So it seems that to be consistent, emitting the canceled signal will need to be a special case.

(Noticed this while testing the tapHandler.qml manual test at some point)

In case gesturePolicy is withinBounds and you drag outside the bounds: it receives QQuickPointerHandler::onGrabChanged(UngrabExclusive) which is also not the same as grab cancellation, but we can say the tap action has been canceled, and that's the intended meaning of the TapHandler.canceled signal.