A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 22 March 2013
As it has been ruled in the past, Plains of the Maiden will net you two separate honor gains if you have any maidens at the battlefield when you destroy a defending army and province.
My question is when you attack a province with Utaku Suying and manage to destroy the defending army+province, will you gain the 2 honor twice from her trait since the stronghold operates that way? Also does the honor gain from their trait stack from having 2-3 of them during resolution of a battle?
Example: I attack a province unopposed with 3 Suyings and destroy it. Will my honor gain only be 5 or will their traits stack to make it 9?
A player, 23 March 2013
Note how the triggers for both cards are worded differently. Bolded parts are mine: Utaku Suying reads:
After a battle resolution in which Suying's army destroyed a defending army or province: Gain 2 Honor.
Plains of the Maiden reads:
After you destroy a province or army in battle resolution as the Attacker: Gain Honor equal to the number of your Battle Maidens at the current battlefield.
Note that Suying reacts to the battle resolution, while the stronghold reacts to the destruction(s). The key difference here is that the army is destroyed at one point of the resolution, and the province is destroyed at another point of the same resolution, so one resolution gives one trigger to Suying but two different possible triggers for Plains of the Maiden.
So, no, you gain 2 honor per copy of Suying, regardless of whether you destroyed both army and province, or only either of them. Yes, their traits stack and can be combined with Plains of the Maiden to gain high amounts of honor in a single resolution. In the example you give, 3 Suyings taking a province unopposed would give you 9 honor (2+2+2 -Suyings- + 3 -Plains of the Maiden-)