Flying to Toronto from BWI--first leg leaves BWI at 5:15AM, connecting in EWR---it's my understanding that the passport check, etc. occurs before the 1st leg--BWI counter opens at 3:45AM per the website....will that be sufficient time?
Not sure you have any other in-person option, unless you've already scanned in your passport, or you check in the night before and spend your evening/night in the terminal.
David