Wanting to and doing so are two different things. Just like the epilogue slides for Orzammar state the Chantry wants to and is considering an exalted march.
That Orlais had plans to take over Ferelden in some matter has never been in question, nor was the possibility that they would try to do so via military means. However, your "solution" was to take them on directly quite soon after the country's forces had been decimated by the Blight and civil war, with no money to fund them, and economics still being so weak they can't properly finances or field an army. Which would be a pretty fail idea in itself: that would be like the Polish army, on horseback with sabres, post WW2, trying to attack and invade a great military and industrial power as Germany was pre-World War 2. Ferelden is still recovering from both a Blight and civil war, Orlais's military is a strong as ever, the country rich and stable.
In otherwords, epic fail for such a plan.
That conflict with orlais would inevitably come is a given. But keeping amicable relations, at least on the surface, would buy time for Ferelden to rebuild it's forces, make very big and powerful friends like Nevarra, and come up with a feasible plan for invasion and occupation of a country the size of Orlais, while behind the scenes working politically and economically to weaken orlais or undermine it in various methods.
At the most, by the time Witch Hunt ends, Ferelden, if Loghain is alive, might be able to fight off occupation attempts from Orlais. But invade? No way. Even if you manage to conscript ever able bodied person in Ferelden into your forces to replace the armies lost at ostagar, from the Blight, and the civil war, you still need an economic system that can equip, feed, and field them all. And, of course, you need generals to train them. Loghain can't really be counted on, since the epilogues state if he survives the whole Blight, the taint takes him in a couple of years, so he won't really be around to help.
The logistics and training issues are the biggest ones, and a poorly equipped, poorly fed army is just not going to go anywhere, especially against a wealthy, well trained, well equiped military like the orlesian one.
As far as Nevarra goes, since they are number 1 on the list for must have allies, what is their situation in DA2? What are they upto, where is their focus,