Search "About Union Station" on the Go Transit website.
The waiting area for sleeping car passengers in the Canadian is in the Panorama Lounge, at the west end of the Great Hall.
I believe CIBC has an ATM in the station, or you can go through the tunnel to the basement of the Royal Bank Plaza for RBC. Follow the PATH signs through the subway station.. TD is at the foot of York Street.
Union Station is in the midst of a massive renovation. A new GO Transit concourse is about to open off the west end of the Great Hall. The existing GO Transit Bay Street concourse is to remain open for now, but is scheduled to be renovated. Also the new Union Pearson Express station will open shortly at the York Street side.