There have been lots of smaller protests in cities across the country for weeks. Tomorrow is the first big push to get people in the streets on a single day. There are 3,500 or more events planned in cities towns and hamlets across the country.
It's impossible to say how many will show up, but I will not be surprised if it's in the one to two or three or four million in total.
Of course it's very hard to get accurate numbers so estimates will range widely.