Most Working Holiday applicants must provide a police certificate from their country of citizenship to apply under International Experience Canada. There are some exceptions, for example, if you are a citizen of Japan, Spain, Belgium, Portugal, Switzerland or France, you do not need to provide a police certificate from your country with your application, however, an IRCC officer may request one at a later date.
If you answered “Yes” to a question about having criminal records from before, you will be required a police certificate no matter the country you are from.
In most cases, you will be able to apply for your police certificates in advance following the instructions here. In some countries, like Hong Kong, you are not allowed to directly request a Police Certificate on your own. You will first need a letter from the Canadian Government requesting you to do so.