I want to try growing some lettuce myself. But note that if everyone grew lettuce in their backyard it would not do anything to reduce winter demand for lettuce (which doesn’t keep all winter).

I was growing lettuce indoors using two Aerogardens. It worked really well, but didn't keep up to my family's needs. I think they offer much larger models now, and that would be an interesting option to run even only during the winter. Of course, you don't really save money when using a system like that, but DIY hydroponic or aeroponic systems can be worth the trouble for some who have the space.

The backyard lettuce revolution would destroy commercial lettuce producers in Canada who only grow outdoors in the summer, while leaving winter lettuce shortages intact.

Nah. Not enough people would commit to backyard gardening. But hey, I'd love to see more community gardens and backyard gardeners growing their own food, especially if they offer up excess to neighbours or local restaurants.

I don't think they would ever be able to put a large dent into commercial producer's business. That would be a good problem to have, since growers can switch crops and diversify what they grow, while communities and individuals fill gaps in food security/affordability.