I think you got misunderstanding with canvas and camera coordinate system (hereinafter referred as cs). Camera cs are built different. It's a Rectangle with start of cs in a point with offset (-1000; -1000) and end of cs at point (1000; 1000).
As i understand it, it's because hardware camera are circled, and sensor itself is a square, and we got rectangle from square projection of circle camera view. (Sorry if it's sounds not so technically as it could)
According to documentation:
The direction is relative to the sensor orientation, that is, what the sensor sees. The direction is not affected by the rotation or mirroring of Camera.setDisplayOrientation(int). Coordinates of the rectangle range from -1000 to 1000. (-1000, -1000) is the upper left point. (1000, 1000) is the lower right point.
also
No matter what the zoom level is, (-1000,-1000) represents the top of the currently visible camera frame. The metering area cannot be set to be outside the current field of view, even when using zoom.