Hi Amahil,
I would like to help you in your quest to find a link between the Egyptian Osiris and a Babylonian/Mesopotamian deitiy, however, I'm rather ignorant of Egyptian myth. Perhaps you could tell me something of Osiris, and i (or someone else) could help you more.
As a start, however, let me say that I am not aware of too many links between Egyptian and Mesopotamian mythology. Thus, I am not sure you are going to find what you are hoping.
With regards to Babylon and astronomy, it is true that Babylonian scholars made numerous astronomical observations. Regrettably, I am not near a library where I can research your question on Babylonians and knowledge of the constellation Orion, though my guess is that they knew of it and passed it on to Greece and Rome. How Egypt fits in is unclear, though again, I am without the resources I need to be sure.
Do write back so that I (or someone) can be of help.
Sincerely,
Ugula, the overseer