Perhaps it was the two people in the tree.

The answer is that the name of this middle part of Dorchester Avenue, which my dad photographed in 1970, was changed in 1987 to Boulevard René Lévesque. The ends of the street maintain the Dorchester name; one end is now Boulevard Dorchester, the other end is Rue Dorchester. Here's the street today. It also appears that Rue Cheneville has been shortened and no longer intersects Boulevard René Lévesque.