This is probably too late to be of any help for you but since I found this post when I was searching for an answer to the same question I figured I'd post what we found at the casino so that the information is available to others.
The Mcphillips Street Station Casino has a huge parking lot with a lot of room for RVs. The lot is next to the train yards but surprisingly it isn't very noisy. We spent the night along with several other RVers. There are shuttle bus stops and the bus makes rounds constantly but it's not a far walk. The casino itself is really nice ( like the no smoking policy in Canada! ) with many machines ,tables and bingo in the middle of the casino.
We're going into the city today to see the Manitoba Museum and will spend the night at the casino again. The city is a little tough to drive around with a RV ,even our small 25' so public transportation is probably the best way to go.