It's impossible to prove the "what if" scenarios, but what we know for sure that the Washington state after the initial outbreak instituted very strict rules and thus avoided a large outbreak, whereas New York state was quite initially lackadaisical and ended up with a large number of infections. Of course, there were also other factors in play, but if you start with a large cast you end up with many casualties. Similar as with growth of governments - large governments grow faster than the small ones.
Fauci already answered that question. He said that of course, if we shut down and isolated from the beginning, there would be less infections. That's obvious. The question is when was it appropriate to do it? A country doesn't shut down because a few people get sick. Honest men can argue over the best point it should be done.
Arguing when it should have been done over and over does nothing for the future. In the US, we're already starting to reopen things; in Canada too where you live. Rather than rehashing the same old things that no one can do anything about, it would be more fruitful if ideas were discussed in how we are going to deal with a very dire future both medically and economically.
For example, the new additional $500 billions the US Congress just passed provides no funding to states that are going broke, including my state of NY who my wife and I depend on for pensions and security retirement plans. How is Canada going to do similar funding when the economies of the world tank into depression. We can't change history. But we all better start thinking about the future because things aren't going back the way they were. It's not just waiters and bus boys who will lose their jobs. It's going to be across the board. As Slobo mentioned about his daughter and other people, there are going to be huge struggle ahead for all groups. Everyone who wants Trump to fail is just shooting themselves in their foot. That's what the whole argument about when we should have shut down is all about. The election. But, if the economies of the world don't get back on track, we'll have more than elections to worry about.