Likely depends on the existing structure of the building - easier on overbuilt masonry structures than newer stick frame / light metal structures. I suspect it's particularly easy in Montreal based on the intended building envelopes on main streets with respect to neighbouring buildings. There's quite a few examples in Toronto as well, though they do tend to displace the existing retail tenants (not always) but also ensure small-scale CRUs remain. These types of structural improvements would also discourage larger land assemblies, at least in the short term. More likely to fly in outlying urban neighbourhoods than right downtown though.
A few I can think of offhand but I know there's more:
https://goo.gl/maps/L2URF1a1EsTxTavq9
https://goo.gl/maps/rELVsTwNds3eUeeNA
https://goo.gl/maps/io8rXUCq1s7s138G9
Of course I've gotten downvoted brutally on reddit for suggesting this idea, because apparently we should be tearing down all of our old retail streets for new condos.