To people saying that Celene doesn't care about miltary matters, remember this:
Celene was planning on marrying Cailan to get Ferelden. Considering that Gaider confirmed that if Cailan survived the blight, he would have divorced Anora and married Celene, that would have meant that Celene would have gotten Ferelden all without needing to use an army. Plus, she wanted to use Ferelden for its resources to battle Nevarra and Tevinter so she isn't dumb about ignoring them. Also, in MOTA, Celene would have gotten the names of every Qunari agent in Orlais had Hawke not interfered. In other words, had nothing gone wrong, Celene would have gotten Ferelden and the names of every qunari agent in Orlais all without needing an army. Can Gaspard match that?
I'm not a political expert about the DA universe but I can't see the Fereldan nobles sitting there and not raising arms with an Orlesian queen, especialy with Loghain alive and Anora, who is respected by commoner and noble both, pulling in favors and working her political magic. As for MoTA, while I don't know the specifics, I don't think we can use thwarted plans as a plus. Would have, could have, should have are irrelevant.
I'm neutral on who rules Orlais. I don't think either Celene or Gaspard is better or worse than the other but as a staunch Ferelden I'd rather put the worst one on the throne which would be...Briala?