I don't want to suggest that you are wrong, but the fact that Osiris is green and has a wife is hardly proof that the Egyptians were making contact with Celtic Britain and the Norse.
The Green man of Britain and Celtic Europe is radically different from Osiris. He dances around, is mischevious and is a spirit of the forest. Egypt has no forests, and Osiris is the judge of the dead. You can't really get much more serious than that. He is green only because he taught the humans to farm, and because he is essentialy a corpse.
However, I feel it is bad to only argue one way, so I will try to give you some evidence to support your idea. The height of the Celtic Empire was around 270BC, and at this time Celtic civillization could be found as far afield as Asia minor. During the sacking of Rome it is quite possible that the Celts assimilated the concept of Isis and Osiris, and withdrew it when the Eastern parts of the Celtic empire were taken over.
To further support your claim, Tammuz, the Sumerian-Celtic Green Man is born in the Spring, loves in the Summer, cut down at the Harvest, and spends the Winter in the Underworld only to be reborn once more in the Spring. Osiris, Green man, Underworld? Lots of connections here, aren't there. Also both Osiris and Tammuz were gods of beer and brewing. And they were both green.
It is my opinion that the Cetic Green Men of Britain and Ireland cannot possibly be linked to Osiris. However, the Green Men of Sumeria and Asia minor could have some sort of link.
It is clever point that you noticed. I wish you luck with this work you are doing, and will try to help you find some more concrete evidence. It really is quite a neat idea.