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The solution completely depends on what your goals are. Are you investing in those tag pages? Is there a reason to keep them around? If you noindex as the others here suggested, you're not only not going to rank with that page, you probably won't with the other. I'd decide what you want to support (it seems categories) and redirect the tag pages. Second best option is a canonical, but then you still have the support the tag pages, the search engines might not respect it, and you're putting a bandaid on a bigger wound. Hope this helps you think through it!