The guy, who tweeted this is pretty much overreacting and trying to spread panic.
The Canadian economy might enter a recession, but I don't expect a financial disaster and a "great depression". Canada has lots of natural resources and there will always be a global demand for natural resources. The Canadian economy is deeply connected to the US economy and I'm sure that the USA will get out of the recession very quick.
The only way to profit from a recession is to wait for the asset prices to drop and then start buying. I'm not a big fan of shorting, because there's higher risk involved. It's way safer to just wait for the prices to drop and buy the dip.
I completely agree with you, shorting a currency no matter how bad it seems is very risky because you never can tell when it will reverse and start going up, the few times I've tried trading futures in cryptocurrency, I've made more profit going long than shorting, so from this , I learnt never to short a currency that is going down but rather , wait for it to go down then long it when I feel it's already in the deep and ready to shot up ..
This same scenario I believe applies to the forex market as well, and besides, speaking about Canada and recession, no matter how bad it seems, I think the country will come out of the recession pretty soon, so personally, if I wanted to make any profit off this, I would rather wait for the deep, then long CAD, rather than shorting it .