Such a claim was never accurate. The regions with good soil are already used. Northern Ontario isn't farmed because of climate, but because it's either muskeg or the Clay Belt. While the latter is good soil, all previous attempts to lure settlers failed because both muskeg and the Clay Belt are completely infested with black flies and mosquitos.
There's been lots of people in the past suggesting that Canada would be a good place to be in as the planet warmed. NOPE!