One of the more complicated GO stations in the GTA is CLARKSON Station in Mississauga (Southdown/Lakeshore).
Drop-offs are super easy, but I don't often get pick-ups from Clarkson GO. There is a parking lot on both the North and the South side of the tracks (See also: KIPLING STATION).
Samuel Beckett's in Shirlington. 5:30 until whenever.
2800 S Randolph St #110, Arlington, VA 22206
Parking garage behind it (set Google Maps for 2850 S. Randolph) and another one by (the official Shirlington Shuffle spot) Harris Teeter. Parking garage: