We at Constant Contact haven't developed any Joomla plugins, but I know outside developers have, and there are many plugins available, such as this or this page of search results. However, most of those that I found only allow contacts to add themselves to your mailing list(s) through your website, not view campaign reports.
We don't support these directly--you would want to go to the developer who created the plugin for specifics of how to install them, but I hope that helps you get started.
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