This tunic dates from the 1920s – 1930s as seen by its construction and George VI coronation ribbon (first ribbon from left; 1937). It was probably used by Hollywood to film movies promoting the Royal Canadian Mounted Police (RCMP) during that time period as shown by the “Martinizing” (American term) dry cleaning tag found in the left chest pocket. Most red Mounties uniforms were not dry cleaned.
The buttons on the chest pockets and the front are all 1 inch in diameter. The epaulets have 0.75 inch buttons. There are no buttons on the lower pockets or on the cuffs since those were added later (after 1953).
In this particular case I have restored the buttons with two 1-inch RCMP King’s Crown buttons (1st and 4th from the top on main closure), 0.75-inch RCMP King’s Crown buttons on both epaulets , and 1-inch Canadian General Service (GS) reproduction buttons from What Price Glory for the remaining buttons. Non-matching buttons are typical of early RCMP tunics due to inconsistent supplies available; many have a mixture of RCMP, NWMP (Northwest Mounted Police), and/or GS buttons.
1 inch RCMP Button Front 
1 inch RCMP Button Back
0.75 inch RCMP Button Front 
0.75 inch RCMP Button Back
The 4 stars are for long service (5 years/star; 20 years total) which is also commemorated by the second ribbon from the left. The sleeve chevrons indicate a Sergeant’s rank. The insignia is bullion wire and dates from the 1930s.
The tunic was found missing all buttons.
Information in this post obtained mostly through email correspondence with the curator of http://www.rcmpolice.ca/