Pretty far but I grew up in MB (north of Roblin). Assessippi is the best ski hill between Alberta and Thunder Bay. I'm not sure if Falcon Lake ski hill (just into the MB border from Ontario) is still open, and haven't been there, but it looks like a great prov. park more similar to ON than MB.
However, the best ski hill around used to be Aggasiz before they closed years ago. There is a small local resurgance to re-open but funds are limited and it is currently located in a national park so the red tape is drawn out. If you study a topographic map of MB, the most "mountaneous" terrain will be anywhere on the Pembina Escarpment - the eastern, steeper slope of the mid-boreal uplands (the mountains in the area). These include, listed from south to north, Turtle/Riding/Duck/Porcupine/PasquiaHills. That order is also the same for snowfall, as the further north you go the more snowfall increases in that range.