My professor cancelled research for the summer, unsure what to do
It doesn't really matter why he did this, and it doesn't really matter to you that it might be unethical for him to treat you this way. What you need is a solution that will advance your studies. 

I think the best advice he gave you is to find someone else. Do that. He may not be suited to advise anyone, and he certainly isn't fitted to advise you. 

You have, I suspect, made some progress on the tasks that he gave you. Talk to other professors explaining what you have done and asking whether they will take you on as a student. You can also explore whether any of the work you have done is useful if you work under their supervision. Don't press it, but it is possible you can leverage it. They know what they are interested in, and you want to become part of that, rather than necessarily continuing what you've been doing. But the work you have done can be used to show seriousness of purpose to a new professor. 

What you want in a professor is someone senior enough that he or she will have plenty of ideas, but also someone who will have the time and desire to help you advance. Very junior professors are too often working too hard to get tenure to be of sufficient help to students. But someone who advises too many students will have little time for you. 

Also, it would probably be a mistake to complain about your treatment by the other professor, except to someone of real authority. As a student, you are unlikely to know what sort of politics there is in the department and speaking out, even if valid, might do you more harm than good. All you need is a solution. Focus on that. If you need to yell and scream, yell and scream at the moon.