If it's going to be published in America, then it should be written from left to right. It has to appeal to Americans, after all, before an agency will take a chance and allow it to be published in another country.
The only reason any manga is in right to left is because it was originally japanese and then translated, and flipping the artwork would ruin stuff like onomatopoeic kanji. Most native english speakers have a lot of difficulty reading right to left, even if they know they're supposed to. Even if someone can read right to left and not get their panels mixed up, most people will still interpret artwork from left to right and ruin the proper sequence for themselves.
If you are publishing in an English country with an English publishing country, make the pages the way all native English speakers will naturally read them. Do not alienate part of your audience for the sake of authenticity.