The June 17 1929 edition of the Toronto Daily Star contained this advertisement for an ambitious retail project.
The Grand Central Market appears never to have gotten off the ground: either it was a casualty of the economic downturn caused by the stock market crash or it was too ambitious a project to pull off.
There is no reference to the Grand Central Market in either the 1929 or the 1930 Toronto city directory. The corner of Yonge and Severn was 835 Yonge and that building is listed as vacant. 159 Bay Street was a relatively new office building, and I could find no reference to it there either.