The provincial government of Ontario has released a document specifying what Stage 3 entails: Click here for a PDF of this document.
It will be of interest to people residing in Northern and Eastern Ontario, as well as some less populated areas of South-Western Ontario, where Stage 3 will be implemented on July 17th, 2020.
In regards to live performances/concerts, music lessons, record conventions and fundraisers, these will still be subject to gathering limits and physical barriers, as defined by local health authorities. And masks will be required for both staff and patrons in the above-mentioned establishments, with social distancing.
Movie theatres in Ontario will probably open with the aforementioned gathering limits, physical barriers and requirements. But Cineplex, Landmark Cinemas and Imagine Cinemas have yet to issue statements on when these will open.
You should note that nightclubs will not be re-opening yet anywhere in the province, nor will dancing or karaoke be allowed because these were determined to be high risk. And I suspect these will not be opening across the country for some time.
By the way, disposable face masks are available from Amazon.ca, Living.ca and your local Giant Tire Store.