It is valid for one year only as per https://travel.state.gov/content/travel/en/us-visas/Supplements/Supplements_by_Post/MTL-Montreal.html
”f you are older than 16 years of age: The original police certificate from your country of current residence, any countries where you lived for more than 12 months, and any country where you have been arrested. If you previously submitted a police certifciate to NVC, it is more than one (1) year old, and you still live in that country, you must obtain and bring a more recent police certificate to your visa interview as the one you previously submitted will have expired. You can find information on when police certificates are required and how to get them on our website.”