ive not fished for browns as much in Canada as live too far north, but spend a bit of time every year, in the Country of my birth New Zealand, the brown and rainbow trout, being the primary freshwater fish,
the vast majority of brown I have caught have been on nymphs, hare and copper and pheasant tail being the most common, or in deep mountain rivers a tungsten been head, modified nymph pattern,
In my view, presenting the fly correctly, on brown out weighs pattern or type of fly, they will eat anything, but can hone in on a food source at times,
My greatest day on brown trout was on a mouse fly imitation in Nelson lakes, they were mice falling out, of the branch's of the beech trees, into the lake, so a deer hair mouse fly was the call, several big browns, ranging in size 3-8lbs for the evening,
Ive had multiple big fish, days on cicada's, and nymphs, and also on streamer's in river mouths, for sea runs, but general found big browns are hard won,
Ive really been struggling, with dialing them in in the area, I have my house in Taranaki New Zealand, they there, I catch the odd one, I can get several nice ones a day, (3-7lbs) a couple hours drive away, but ten minutes from home, not so much. difficult fly casting conditions being sum of the problem.
I think your fly above, is too sparse in the body,
switch to a brown or black leach, mudder or Matuka, and fish it bouncing of the bottom, Good luck, a worthy goal for the summer,
Mistry creek, perfect nymphing water, nice brown in this small run, but i fluffed it up,