Seems to me a question of how far the door is opened is the critical factor.
Taking the previously mentioned flat plate theory, (as any aerofoil considertions are not relavent as we don't have an aerofoil, only possible disturbances to flow), the Cessna will be influenced to yaw right or left depending on whether the normal force on the door passes fore or aft of the aircraft c of g, and this would depend on the door opening angle.
What ensues next is in the domain of the aerodynamicists.
Seems to me it depends on the angle to which the door is opened.
Following the flat plate theory, as I do not believe the door is an aerofoil, although it might well be a spoiler, if the normal force on the door passes fore of the cof g, the plane will tend to yaw left, if the normal force passes aft of the c of g, it will yaw right.
What the plane subsequently does is the realm of the aerodynamisists.