Visiting: Labor Day Weekend in Downtown?

I live about 3 hours from Chicago in Iowa and we have 2 friends up from Brazil that we want to take to Chicago on the Sunday of Labor Day weekend. Can you please give me any advice on what to do/see and if there is anything major (festivals, concerts, etc) going on that weekend that we should look into or that would cause crazy traffic.

My thoughts were to go to a pizza place, Navy Pier and possibly Water Tower. We have Marriott points so we'll try and stay at one of those but nothing is set and I'm not very familiar with downtown (we usually stick to the suburbs).

Thanks!