Initially, Share your research proposal with a most appropriate research scholar. I suggest the easiest way is to, prepare a directory of researcher you are following or reading their literature. Then ask the same authors for collaboration, with an aim to enhance the scope of their study. They will definitely collaborate and your proposal will be on the right track.
Collaborations almost never start with a cold email. All collaborations have involved people from same lab, or people you met at conference. I think you have to have something the other side will obviously want: a dataset, a method, a tool; access to a site or species or specimen; something besides an idea. Lots of people have ideas. Lots of people even have the same idea. But in order to start a research relationship with someone you don't know, you've probably got to have something they want and vice-versa.
For collaboration, 2 researchers must have a common research interest. Social networks provide an excellent opportunity for interaction between researchers coming from various parts of the world so it can also be used as a medium to initiate any collaborative association. I will end by saying that any researcher from any field of science is usually happy to be in a symbiotic professional relationship.
First look the common things that are between you both. Then from there you may start. Joint publications, applying for grants together, supervise students together and etc.