Folk with much more expertise in uniforms of the period who I have consulted on and off line elsewhere are unanimous that the uniform is US military or at least US military based, confirming views expressed here. The kepi style cap, slightly obscured by the ornate plume, the triple row of buttons, the cuff adornments and the shoulder boards are all characteristics found in US uniforms of the period and most certainly not on British (or Canadian) uniforms.
The belt buckle if identified may link to some specific organisation but otherwise Regorian has it in spades.
MaxD