The bus terminal used to be along Graham Avenue, before it moved by the U of W in the 60s.
Here's a picture from 1961, towards the end. I can't imagine that the terminal was very old at that point, maybe no more than about 25 years old or so?
Source:
http://home.cc.umanitoba.ca/~wyatt/alltime/pics/winnipeg-commuterbuses.html
I have no idea what was there prior to that, but I'd imagine it was probably just residential houses or small wooden commercial buildings. I don't think there was anything there after that... it has literally been a surface parking lot for a good 50 years or so.