Grew up in the Beaches and have lived in Leslieville since 2003. I hate these debates, as Leslieville was never incorporated and has never had truly defined borders. It's usually real estate driven - bleh.
However, for the sake of chatting about it - from living in 4 different addresses in the area and speaking to folks around much longer, this Google map definition is pretty good and makes sense. The train tracks are definitely the Northern boundary. As residential begins to blend into Commercial/industrial to the south it creates a southern edge. In the West, I understood that Logan was the line where Leslieville ended, leaving a small patch including Booth and Empire as orphaned territory between Leslieville and the so called Riverside on the other side of the tracks. To the East I had never thought I would call anything beyond Greenwood Leslieville. However, the area between Greenwood and Coxwell certainly fits the neighbouthood profile of Leslieville versus the Beach to its East.
I am now living at Broadview and Queen and out of habit and fondest I still pronounce myself as living in Leslieville - Terrible I know!