So the visitor visa (TRV) is a travel document, whereas your status in Canada is another thing altogether. It's entirely possible that you could be admitted for six months as a visitor even though your TRV is expiring in less than 6 months. I don't know that it's likely, but it's possible.
But if you need to stay here 6 months, yes you should renew, but try renewing a little closer to the expiry date. I'm not sure they're going to let you this far out, unless it's a Super Visa.