Can lottery winners remain anonymous in Ontario?

No, lottery winners in Ontario cannot remain anonymous.

Here is the excerpt from the OLG FAQ for more details

The publishing of winners is important in demonstrating the integrity of our lottery games. OLG reserves the right to publish the name, address and photograph of any winner. This is necessary for us to demonstrate that people do win. Winner information is released to the news media and may be used in OLG 's advertising. For every prizewinner there are a number of other players who did not win but have a legitimate desire to know that someone won.