Hi seemsartless,
This isn't "Glen Castle", what it might be I can't be sure. There was an "
Ansley Castle" at the corner of what is now Glengrove and Heather, on top of the low hill just east of the present day John Ross Robertson School.
If you can find a copy of Don Ritchie's "North Toronto" (Stoddart 1992) or a copy of "North Toronto in Pictures" (Toronto Public Library Local History Handbooks 1974). there are pictures of Ansley Castle. Time prevents making scans this evening.
From "North Toronto" page 88: "...the 'castle' had been built for Alfred Ansley, a successful manufacturer of hats..."
From "North Toronto in Pictures" page 19: "...the Ansleys built a substantial house of Portland cement at Heather street in 1909. When demolished in the early 1920s, the neighbours took pieces of it as souvenirs and used it for rockery in their gardens."
More on Glen Grove Park from "North Toronto in Pictures" page 19: "Pilgrims Farm [the name for the area before it became Glen Grove Park] was settled around the time of the War of 1812. James Beatty, a later owner, made it an 'occasional summer retreat' and renamed it 'Glen Grove'. Glen Grove Park was a popular place for Sunday School picnics and church garden parties in the 1890s.The open fields near Yonge street were used as a race course, a baseball diamond, an a cricket field."
I agree with your guess that your picture scene might be on the east side of Yonge - Blythwood Ravine. I could be wrong but I haven't been on Glengrove Avenue east in decades; it's a short no-exit street and I have no reason to be there but I don't think there is an extant house like that.
You have a nice website by the by.