Gary Johnson's position, if he is consistent with his own prior statements, would be that he is opposed to Roe and understands that the Constitution does not mention abortion at all, i.e. 10th Amendment, i.e. federalism, i.e. return the matter to where it belongs by the rule of law, with each state setting its own criminal code in this regard. This would theoretically mean he could be trusted to appoint non-corrupt and literate Supreme Court members.
That said, IF he is consistent... Well he isn't - see this video, 20 seconds in, or his current campaign website makes no mention of this instead adopting either defeatism or support for the status quo.
As such, he isn't qualified to be making those appointments, period. Not that Trump with his lifetime of public statements and donations is qualified now that he gives lip service. And of course Hillary is just abject scum.
The Doctors Paul I would happily vote for and have in primaries whenever possible. Bob Barr or Michael Badnarik were worth supporting. Johnson... Ehhhhhhhhh. No.