http://bibnum2.bnquebec.ca/bna/lovell/index.html - in 1906/1907 and in 1907/8 directories, at 542 Lansdowne Ave is listed 'H. R. Hutchinson of J. H. Hutchison'. (J. H. Hutchison is probably the name of a familyshop/company). At 551 is Wm Campbell, W. R. Campbell, and H. M. Campbell.
Looking at google map this seems to be a residential area, which is borne out by the directory - at 305 there is the Westmount Methodist Church. Both the addresses are near the intersection of Lansdowne with Chemin Côte St-Antoine.
In 1910/11 Wm Campbell is still at 551, 542 is occupied by J. MacEwen.
In the census I believe this area is listed as "Westmount". In 1911 551 Lansdowne is at:
1911 / Quebec / Hochelaga / 50 Westmount / page 15
At 551 is a family headed by Frederick Gordan Payne, accountant, aged 60. + two sons. There is a housekeeper in residence. Judging by his and the neighbours' occupations, the families in this area were reasonably well off. Not all, but several have domestic live-in help.
542 is at:
Home / 1911 / Quebec / Hochelaga / 50 Westmount / page 21 split view
Living there is John MacEwen, his wife and children. He is a manager (place of work: fine m?
), and his nearest neighbours are an architect and 'assist. to vice president (railroad)'. Again, several live in domestics in the area.
Presumably whoever was organising work for the home children was kind enough to try and place them together.