The application cannot find the pulseaudio library, because it’s in a subdirectory that’s not in the LD_LIBRARY_PATH. Use the snippet below (which I have corrected) which will add the path in which the pulseuaudio library resides, to the LD_LIBRARY_PATH.
apps:
white-canary:
environment:
LD_LIBRARY_PATH: $SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pulseaudio
The previously posted snippet was incorrect.