There are a few attendings out there, but these are outliers and do not treat these as the norm, because the process in how these attendings are able to be faculty are very, very, condition and state specific.
For academic centers, the center has to file an exception to the ACGME accrediting bodies due to some sort of hardship or for an exceptional candidate (typically a well known big wig internationally). The VA is a bit more forgiving, but similar situation. If you did your residency in Canada, your chances are much better (I think there is some reciprocity between the US and Canada regarding training).
The big hold ups are this:
-Board certification (
Requirements for Certification | American Board of Ophthalmology). If you want to be board certified, the requirements specifically state finishing a US or Canadian residency. 20-30 years ago, board certification wasn't a big deal, but nowadays if you want to bill insurance, it's a necessity.
-State medical licensure: each state is different but you have to fulfill that state's requirements to obtain a license. Some of them (including mine) specifically state you have to do a residency in the US in order to have a license. No license, no practice.
-Supply and demand. Most places aren't so desperate to hire someone who hasn't finished a residency in the US or in Canada. There are some exceptions in big cities, but they are almost always in fields where there is a large predominance of IMG/FMGs (neurology, psych, etc.).