So much ignorance here.
1) The project is not going West of Downtown Toronto right now. You can blame most of that on Metrolinx and the failed Ontario HSR plans, which basically ruled out federal HSR expansion West of Union. At best, if they go West, it's to Pearson and it's because they are using the Midtown Corridor. That's a stretch right now.
2) Take a map. Draw a straight line from Ottawa to Montreal. You're going to see that Laval is on the way. And it's the Mississauga of Montreal. Either way, Laval is en route either from Ottawa or on the way to Trois Rivieres. Ergo, it was always going to be served. Square One is not on any rail corridor HSR would use.
3) The very fact that you think adding Ottawa is a chore shows you ignorance. Both air and rail traffic between Toronto and Ottawa and Toronto and Montreal are relatively close. But boys who only travel to Montreal for Bachelor Parties will not understand how much business travel there is between Ottawa and Toronto.
4) If Mississauga is getting served, it will be at Pearson station. Nobody is diverting the train out of the way to serve Mississauga. And if the downtown station is at Union, it's really easy to take GO and get on an HSR at Union anyway.