Preheat oven to 375°. Wipe chanterelles with a damp cloth or scrape with a knife to remove dirt; cut away dry, woody parts. Tear mushrooms into 1-in. pieces.
Cook pancetta in a large frying pan over medium-high heat until crisp and browned, about 7 minutes. Transfer with a slotted spoon to paper towels, reserving drippings.
Toss potatoes with 3 tbsp. reserved pancetta drippings (see Notes), garlic, thyme, 1 tsp. salt, and 1/2 tsp. pepper. Divide potatoes between two 9- by 13-in. glass baking pans. Bake, stirring every 10 minutes, until tender, well browned, and crispy, 25 to 35 minutes. Remove from oven and keep warm.
Melt butter in a large frying pan over medium-high heat. Add shallot and cook until soft, 1 minute. Add mushrooms and cook, stirring occasionally, until browned, 5 to 6 minutes. Add Chardonnay, remaining 1/2 tsp. salt, and remaining 1/4 tsp. pepper; scrape up browned bits and cook until liquid evaporates, about 2 minutes.
In a large bowl, toss together potatoes, mushrooms, pancetta, tarragon, and chives. Drizzle with vinaigrette. Serve warm, with fennel-spiced wild salmon.