It's possible for both dialects to evolve, but at different rates. Present-day Quebecois French is not identical to 17th century French, but it's closer to it than present-day Parisian French is.
You can't just make that kind of statement as a fact without providing any kind of source. Read any text from 17th century, languages have evolved quite a bit on both sides of the atlantic.
One big reason why Parisian french would be quite different is that colonization to New France did not come from Paris.
People say this, but I've always thought it was just another piece of pop badlinguistics nonsense that you hear about practically every language. Do you have a reliable source?