There is no change in addition to what can be seen and the limited actions that can be performed on the question once it is closed. Changing the canonical meta tag might not be a good move. I mean, the content of one page and the duplicated one can be different, in practice. Even in terms of how the question or potential answers are spelled.
It would even make more sense to perform an HTTP redirect rather than the meta tag change.
However, if the page doesn't receive too many views (which should be the case considering there already is another similar question) the best thing to do is to hide it.