Melt the butter in a large saucepan. Add all but 1/2 cup of the fennel along with the sliced onion, garlic and fennel seeds. Cook over moderately low heat, stirring, until the fennel is crisp-tender, about 20 minutes. Add the fish stock and bring to a simmer. Cover and cook over low heat until the vegetables are softened, about 20 minutes. Let cool slightly, then puree in batches in a blender.
Strain the mixture through a fine sieve; discard the solids. Pour the broth into a small saucepan, add the Pernod and season with salt and pepper; keep warm.
Using a sharp knife, peel the orange, removing all of the bitter white pith. Working over a bowl, cut in between the membranes to release the sections. Add the celery, red onion, olive oil, vinegar and the reserved 1/2 cup of fennel to the orange sections and toss. Season with salt and pepper. Spoon the mixture into 4 shallow soup plates and let stand for 15 minutes.
In a large skillet, heat the canola oil until shimmering. Pat the scallops dry and season with salt and pepper. Cook the scallops over high heat until browned and crusty, 2 to 3 minutes. Reduce the heat to moderately high, turn the scallops and cook until browned, about 2 minutes longer. Arrange 3 scallops in the center of each soup plate and spoon a little broth over the vegetables. Garnish with the chives and feathery fennel tops and serve.