I definitely do
not recommend showing the 9.
How can you be so sure that he has the flush? If his raising range pre-flop is tight (you haven't given any indication otherwise) then the only possible holding he could have here would be A
J
or maybe A
10
. Do you think he would raise A9 or less or other suited connectors?
If his raising range is tight then boats are in his range as well as AK. I would make it $30-$35 here on the flop. If checked to on the turn again, I would lead about 70-80% of the pot size so when villain donks into me for such a small amount I ask myself if he normally bets 1/3 pot and consider raising.
Given your passive player here, he might be betting AK for value OOP on the river, as well as made hands that dominate yours.