Asking for Editor comments even before submitting to the journal, Is it ethical?
I don't believe there is anything unethical in asking. You are just getting an opinion, if anything. Of course, the editor may decline as it may raise ethical issues on that end, but not on yours. You aren't asking for an advantage over others, but just advice on suitability. That is the editor's function, though they may prefer, and have rules, to only comment on proper submissions. 

He has seen the paper already, of course. Some editors would actually encourage you to submit it without even being asked. It will be judged by reviewers other than the editor, of course.