Ethiopia in my opinion would no doubt win. I have upset Egyptian aquanitences with this opinion, but Egypts military is a paper tiger. There is a reason why Ethiopia does not submit to Egyptian demands - Attacking would be suicide, getting past Sudan and such. The world would take the side of the defenders, and likely results are Sudan gets that disputed territory, and Egypt is subject to humiliation. Empty threats have been made for years. Still, it is an interesting idea. I think that Islamists would take it as a sign of weakness and attack Sisi for being weak and the copts for being traitors.