I don't think that a transportation network attract people to a particular city in any great numbers. People migrate to a new city for job opportunities or social reasons, not because they like to drive or take trains. However, the transportation networks play a role in where those people choose to live within the city. If the city is automobile-oriented then the city needs to be highly dispersed. If the city is transit-oriented it needs to be highly concentrated and walkable.
Projects like the Hurontario/Main Street LRT will allow Mississauga and Brampton to start building larger, more concentrated, developments along the corridor. The flip side of that is when it comes online there will likely be less low-density development pressure in neighbouring Caledon and Milton. If people have a choice of living near the LRT in Brampton or commuting by car from Caledon, some people will choose Brampton. Right now they don't have that choice. When the Eglinton Crosstown LRT comes online there will likely be a some shift of development to the Eglinton corridor. If the Crosstown wasn't being built that development would go elsewhere in the GTA.
So to say transit "generates" new development is probably incorrect. It just redirects development within the community.
Transit may or may not have a role in attracting new businesses to a city.