You should read some Jane Jacobs for more details, but the economic drainage and "provincialisation" of Montreal (and other eastern cities) to the profit of Toronto (in various respects) is a direct consequence of the union. For example, most financial businesses moved to Toronto from MTL, exchanges are all there. We also lost our dominant place in air travel to the profit of Toronto. And on and on. Basically, the union has a cost.
Here's a quite unknown book she wrote about it: https://www.amazon.ca/Question-Separatism-Quebec-Struggle-Sovereignty/dp/1926824067. As Philpot says in the foreword, her book is not discussed by "anglos" because they don't agree with her (vindicated) analysis of the situation.
Si ça vous tente d'en apprendre un peu sur l'histoire des développements autoroutiers dans les villes Nord Américaines, mais surtout sur l'oeuvre de l'urbaniste et philosophe Jane Jacobs, TVO a cet excellent documentaire gratuit en ligne Citizen Jane: Battle for the City
... et c'est aussi une des seuls intellectuels anglo à soutenir le projet d'indépendance du Québec