No Canonbury Avenue.
Google was not a significant help, either. However, it did point the Gorse Fox at the Charles Booth archive held by the LSE. There, deep in the recesses of his notebooks, the Gorse Fox found the clue he sought.
"the open space on the map north of Canonbury Square is now occupied by Canonbury Avenue - 2 rows of buildings next to the Board School. 4 Stories - working class; paved passage down the middle"The Gorse Fox can now rest. The mystery is solved. He no knows where the McDonald side of his family lived in the 1890s and early 1900s.