The final hurdle I see for your friend, besides
(1)avoiding elimination on the ATP application for moral character,
(2) passing the FAR 107.209d requirement for SIDA access, and
(3) dealing with the Canadian travel issue
... would be whatever Human Resources / Employee Policies are in effect with a given employer.
Some companies are pretty strict about past criminal activity. Most write their policies very strictly but may not be so strict in application to a given situation. It gives them some flexibility. I think a lot of them, however, are willing to overlook an offense depending on what it was, when it occurred, if the person is HONEST about it, and if he appears to have learned from his errors and chosen a different direction for his life.
He just needs to realize that regardless of whatever career track he pursues (airline or other), that his past mistakes may continue to haunt him for a long time as part of the consequences of his bad choices. Eventually, he can recover from it but it will take years of good behavior to demonstrate that he has changed. Maintaining a positive attitude about it may be difficult but is critical so that when the topic comes up it can be dealt with in a constructive way.