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That's good solid advice. Thank you. Other ecommerce sites in the niche are nothing to write home about. Where they win is where this site has some major issues (larger than the one I'm asking about) that need fixing too. I'm just trying to come up with a cohesive plan for a site that will blow the competition out of the water on Google (achievable) and increase sales / visitor. This is part of that. Much as I don't like your suggestion due to the amount of work it is going to take to implement, I do think you are right and it's a better solution than the canonical tags. That said, I suspect the canonical tags will be tried first, and then we will end up going with the content writing.

I have conformation directly from Google's John Mueller that this is not a problem and the penalty will NOT pass between domains with hreflang.