Complex sentence: As both the Northern Railway and Great Western Railway had been acquired by the GTR, this was not a true Union station, however the Canadian Pacific Railway began using the facility in 1884 and it was completely rebuilt, opening in 1896.
Split into simpler sentences: As both the Northern Railway and Great Western Railway had been acquired by the GTR, this was not a true Union station. However, the Canadian Pacific Railway began using the facility in 1884 and it was completely rebuilt, opening in 1896.