This is the kind of area that you go to without a specific plan. "What are we doing today?" / "Going to the Atwater Market area". That's it, your plans are done.
It is a charming, picturesque area regularly flooded by Montrealers on a nice day. The corner brings together the Atwater Market (produce, flowers, meats, cheeses, etc.), a large outdoor public space (seats, tables, sandbox for the kids, public piano, buskers, musicians, outdoor photo exhibit), outdoor-specific business (ice cream, boat & kayak rental, bike rental and servicing, etc, etc.)
Again, you just go there, and your day will be full.
138 Avenue Atwater, Montréal, QC H4C 2H6, Canada