HI There
The BA lounge at YVR offers no discrete/quiet place for a nap and is pretty crap in all regards IMO.
The plaza premium lounge has IIRC 3 dedicated daybed-type rooms with comfy loungers, low/no lights etc. This lounge is always pretty quiet with far better food offerings than the BA lounge.
The CX lounge hasn't been open whenever I've been at YVR so I can't comment on that.