An update: we now know all but one team in the 3rd qualifying round of the CL. (The as-yet unknown team will come from Greece and could be either PAOK, AEK Athens or Panathinaikos).
So the League Route part of the third qualifying round will look like this:
SEEDED--Shaktar Donetsk, Ajax, Anderlecht, Fenerbahce, Sparta Prague
UNSEEDED--Steaua Bucharest, Monaco, Young Boys, Rostov, Greek representative
The five winners of those matches go into the Play-off round.
If the seeded teams in the 3rd qualifying round all win, the Play-off round would look like:
Manchester City, Porto, Shaktar Donetsk, VILLARREAL, Ajax
Andelecht, Roma, Borussia Munchengladbach, Fenerbahce, Sparta Prague
Within each group, these are listed in coefficient order. Therefore, should Shaktar and/or Ajax lose their third-round match, Anderlecht and/or Roma would move up to be seeded teams. If Shaktar and Ajax both lose, and Anderlecht also loses, then Gladbach would become a seeded team along with Roma. That's probably not too likely.