How can I do the correlation between two estimators? I'm working with several estimators of all kind. Then, I want to stack these estimators, and the best is if they have low correlation between them.

I suppose that the correlation method depends on the type of dependent variable, if it's categorical or numerical. In my case, it's categorical, and the estimators are classifiers.

How can I do the correlation between two estimators?
There are probably many options, I'd look at inter-annotator agreement.

An alternative option would be to to evaluate one (e.g. by accuracy or f1-score) using the other as the gold standard.