One of the only place to get electronic components, connectors and wires easily in Montreal. There is no such places as Fry's Electronics in Québec so there no places where one could get it all but at least part of it can be found at Addison.
One thing is certain: Don't buy ready-made cable at Best Buy, Future Shops or La Source, come to Addison, you'll pay way less and have a better choice (I always have the feeling that electronic store make their profits on cable).
You'll also find network cable and equipment here.