Gas stations have always been in big demand in the US and Canada especially from new immigrants searching for a job replacement. A gas station is perceived an easy business to manage not requiring neither sophisticated management skills nor high English fluency skills.
This large demand had driven prices very high to the point where an investment in a gas station rarely provides a reasonable return on investment when you compare it to other business opportunities. Nevertheless, demand will continue to drive prices very high as long as new immigrants with large amounts of cash available to invest come to North America.
This however does not mean that the purchase of a gas station is always a poor investment. A large part of gas station transactions include the sale of the land, which land is generally located strategically and do appreciate significantly over time. The large land value component of the transaction also reduces the investment risk significantly making up for the low return on investment.
As a result, when looking at the bigger picture, the purchase of a gas station that includes land could end-up been a great real estate investment instead of a business investment.
From an operations perspective, the supply of gas is very concentrated in Canada in a small number of suppliers who call al the shots leaving very small survival margins to gas station owners. The sale of gas becomes almost a loss leader for gas station owners who make most of their profits on their convenience stores attached to the gas stations.
The best method I can think of to find gas stations available for sale in Ontario, Canada is to search the business for sale magazine "Business Exchange" that is available for free in most Real Estate offices, especially those who have agents selling small businesses. This magazine contains a large list of gas stations listed by many real estate agents who specialize in the sale of Gas Stations.