I believe it is Hosokawa-nioi in bloom on the alley (east) side of the Laurel Point Building, 1518 W. 70th (west of Granville). Very fragrant, large flowers as big as Tai Haku. Extra petaloids visible. Style and stigma shorter than longest stamen. Long, narrow sepals. Looks like the one in Kitsilano. Wendy's post here: http://www.botanicalgarden.ubc.ca/forums/showpost.php?p=196018&postcount=50
Douglas Justice has not bought this as the ID (yet?), so I've copied this posting over here to try to confirm an ID. He suggested in an email that we should consider 'Jo-nioi'. I don't know if it's just because these flowers are just opening, but the petals seem more round than in the 'Hosokawa-nioi' photos in this thread: Hosokawa-nioi? Semi-double white, fragrant, late mid-season and in the 'Jo-nioi' photos in this this one: 'Jo-nioi', was Unknown white semi-double cherry, late-blooming Well, Joseph Lin's photo in the 'Jo-nioi' thread does show quite round petals. I'm not seeing stipules in the 'Hosokawa-nioi' photos, but maybe we just need more photos. Stipules here look similar to the 'Jo-nioi' ones. In both of those threads, the leaf photos show a lot of red glands, which I'm not seeing in Anne's amazingly clear leaf photos here (amazing considering the location of this tree behind that wall).
Here's a 'Hosokawa-nioi' photo from 2010, posted in the neighbourhood blog. It's showing the flowers out before the leaves. The tree in question in this thread, and the 'Jo-nioi' photos show leaves with the flowers. Also the popular flower arrangement on the 'Hosokawa-nioi' seems to be what the term "peduncled umbel" must refer to, the group of four front and center not withstanding. Is the absence of red glands a show stopper for an ID of 'Jo-nioi'?
Here is Laurel Point's east side tree (W.70th and Granville) one week later on April 13, 2013. The second row of pictures are of the two Shirotae trees on the west side, on the same date, to compare the aging.
I posted some new photos in the original Hosokawa-nioi thread, including one of stipules on a non-flowering set of leaves on the trunk.
Here is the Hosokawa on Burrard and Cornwall in bloom on April 15, 2013. The tree in Marpole does not look like it and the Hosokawa leaves are serrated differently too. I saw a young Shirotae in the same park at the NW corner of W. 1st and Burrard on the same day and the last three photos are of it. This young tree had fragrant flowers. The petals on its flowers are not as numerous as in most Shirotae trees I've seen. In fact, they appear as few and as flat as the flowers of the tree in Marpole. The leaves are very similar too. Given that the Laurel Point complex had two Shirotae trees on the west side, maybe the tree on the east is also a Shirotae.