According to page 4 of
this pdf on the history of the Curry Building (233 Portage Ave), it was originally "intended to be the base of an eight-storey retail/office tower". Interestingly, it says that reinforced concrete and steel were used as structural materials, which raises the technical feasibility of building those six extra storeys above it today. Avenue Part II, anyone? (Seeing as the Curry building is the eastern neighbour to the Avenue Building).