Based on an assertion in the answer to: " When Can the Dark Side Be Sensed? ":
Is there some canon (ideally, G-canon but not required) information clearly indicating whether Obi-Wan Kenobi know that Darth Vader was on board of Death Star before they actually physically bumped into each other?
If earlier, just when did he find out?
UPDATE: To clarify, "Vader knew when he discussed it with Tarkin" is NOT evidence for or against, unless there's a canon proof that Obi-Wan must have detected Vader at the same time as Vader detected Obi-Wan