You should be able to find the better-known Ontario wines at the LCBO, at one of their own stores, and possibly at selected grocery stores or retail outlets within those stores. Lesser-known Ontario wines can be acquired either by visiting the winery or via an online agent which acts as a middle man for small agencies and small wineries. See below for two examples:
Kwaf specializes in good value Ontario wines from smaller and lesser known wineries which they provide via a subscription service. Every two or three months depending on the service chosen, you will receive a case of 6 new wines. Each wine has a complete run down of information including tasting notes, food pairings, and winery history, and shipping is free.
MyWineCanada is an online agent for wineries across Canada. You can order and pay for a wine online and it is shipped directly to you from the winery. Some wineries will sell individual bottles. Another approach is to join their wine club and receive any of two, three, six or twelve bottles monthly from a designated winery of the month along with tasting notes, wine reviews, ratings, and food pairing suggestions from their Wine Experts.
Many Ontario wineries are located in the Niagara-on-the-Lake region. However, there are an increasing number in Prince Edward County, and some in the Lake Erie and Pelee Island region. For regional overviews and specific information by winery including special events, local cuisine, route maps, day trip, and vacation information, visit Wine Country Ontario, managed by The Wine Council of Ontario, a non-profit trade association for the wine industry in Ontario.