So you're prepared for it to come to war? How should it be fought? Is there a realistic chance for victory anytime soon?
Oh, you want a plan. Okay, we'll need to vote on it, but here are a few ideas:
Shianni got off to a good start when she was named Bann of the Denerim Alienage. She needs to be at every Landsmeet and she needs a household guard, to which she is entitled. These guards will train and be well-armed. They won't start any trouble but neither will they allow any harm to come to the Bann or the Alienage. They will keep the city guard out of the Alienage, reminding them that the Bann has authority within, not them.
Then we open up the Alienage. We establish a Mission to help anyone who needs aid. Food, medicine, a place to sleep, a job, etc. Every elf is encouraged to contribute, but we open it to anyone, elf, human, dwarf, or misc.. Only the most desperate would come to us, but that's fine, that's exactly where we'll find friends. The Mission does not require that you worship any gods, but we invite the Chantry to send a priest to provide comfort to those who want it, as well as the dwarves and the Dalish. This serves a number of purposes: it shows good will, it preempts any claim that we are 'corrupting the faithful', and it provides protection, as any attack on the Mission would also be an attack on a member of the Chantry. Within a year, it becomes established in people's minds that the Alienage is a place for those in need to find friends.
We're still training guards to protect all of this, and they in turn start training civilians to protect themselves in the event of an invasion. We also start training Irregulars. Their job is to spy, ambush, and retaliate against anyone who fights elves or elf-friends. Nothing overt, and nothing that can be traced back to us: shoot them in their baths and run out before anyone sees them. Drop Antivan fire through the windows and get out. That kind of thing. Never fight them on their terms, because that fight cannot be won. Just make it so that fighting us is more grief than it is worth.
We then start training 'Missionaries' to go out to other Alienages and show them how to organise as we have. They won't have a Bann, but they can name their own spokespersons to represent them. Keeping out the city guard is not an option for them, but their militia can guard the guards to ensure that they behave. When clashes inevitably happen and some of our people die, we take note of names, and those guardsmen and their leaders find themselves murdered in their beds by our own Irregulars. Meanwhile, the Missions continue, winning us hearts and minds. Alienages are now populated by people of all races. When you attack the Alienage, you attack more than just elves.
We encourage our tradesmen to organise into guilds. By working together instead of competing, even across cities, they will soon dominate their markets, but again, these guilds will be open to tradesmen of all races, and they will see that it is to their advantage to become members. That gets elves, dwarves, and humans coming together as smiths or tanners or cobblers instead. There will be opposition and they will need to be defended, both by guards and by the threat of the Irregulars.
We start encouraging our people to spread out. Get out of the Alienage, but go where you are likely to find friends. They know you, they work with you, they drink with you, they're not going to drive you out of their neighbourhoods. If trouble does come, you can probably count on their help, and we'll be watching out for you too.
And now we have enough political capital to make demands. We have people in political posts. 'We' are not even 'the elves' any more, we are 'the people'. Our children play together with no thought to their physical differences and have never known anything else. The Irregulars retire and turn to drink to try to forget the worst of it, and our Guard becomes 'The Guard', having replaced the old guard. If we're not too old yet, we can now start an anarchist revolution, or maybe we can leave that to our children.
Obviously it's a rough outline. 