There is conflicting information as to the purpose of this building. Some information seems to indicate that this site was a World War II-era radar site. Perhaps a transmitter site, associated with the large antenna atop the nearby mountain-top.
Other information suggests that this building was part of the communications system assembled by railway that would bring Newfoundland into Canada, and part of the viewership of the CBC. Its proximity to the former railroad does seem to support that.
There will be further updates as I find out more.