Hey there,
Those "Cons" you named are basically your options. Either add rel canonical or create unique content. Technically, you can delete the page as well, but I guess it's not the option you're considering.
It's true that it takes time and effort so this would be probably your decisive factor. Just decide what take less time and is more convenient. I vote for adding the canonical tag.
Regarding the _low search volume, _every visitor is valuable as long as he/she converts. It might be 1 visit a day through that KW but (depending on your conversion rate and the price of what you're selling) I think it's worth it.
If you add "noindex" to your page, Google will still be able to crawl your page and see the duplicate content. So I'd choose one of the two options mentioned above.
Hope it helps.
Cheers, Martin