How to decorate a brown over-sized canopy bed?

What kind of window treatment do you have? You could repeat that style for the canopy if it’s feasible. Or you could go with sheer white scarfs festooned along the rails and draped down along the posts. The white, although neutral, would contrast with the brown and tan and the sheer fabric would not take up space visually. From there you can can still choose any kind of bedding that would compliment the walls and window treatments.