If that was such a "sure thing" i.e. low risk, don't you think all the media would be touting this strategy and everyone would already be doing it?
As for "due diligence", that's an easy phrase to bandy about as a disclaimer. It's a lot harder to do it successfully in practice.
Dividends aren't guaranteed. A company can cut the dividend rate or even the dividend altogether when times get tough. Usually they have to do this because their business is in trouble and/or the economy is in trouble. Either of those plus a dividend cut usually result in a dramatic decline in the price of the company's stock. So you suffer a loss not only on the dividends but also on the principal.
While Canadian banks haven't cut dividends in decades, it could still happen. Indeed reversion-to-the-mean suggests the longer the upswing the more likely a downswing. Besides it's not a good idea to invest money solely in the financial industry. And of course Corus is hardly as secure and low-risk as a big-5 Canadian bank.
Also there have been periods in market history when aggregate dividend yields have been lower than HISAs rates.
See also my comments here and here about why equities, even blue chips, are hardly a substitute for a HISA.