Not been able to find out anymore about Rose & Nellie but I have found some more on Arthur with other Carvers now entering the fray.
1921 Canadian census: 699 Queen's Avenue, London, ONT: Arthur Carver, lodger, 30 [? guess], married, b. England; both parents English, arrived Canada 1906, Canadian citizen, Anglican, labourer; Agnes Carver, lodger, 23, married, b. England, both parents English, arrived in Canada 1913, Canadian citizen; Ernest Carver, lodger , 8 months, b. Ontario, 1920., both parents English.
Whilst the year of arrival in Canada is specified, for ages only a number is given. As for the relationships, the location has several other lodgers and although ADC state 'Head' for Arthur, looking at the actual entry close-up it does indeed say 'lodger' too. The obvious inference to me is that Arthur married Agnes (also from England) and they have a son, Ernest.
Electoral Roll info on Arthur from Sarnia (where Arthur is buried), Lambton West, Ontario:
1957 - Arthur Carver, retired, 893 Hagle Street. At same address: Mr Robert Carver (technician) & Mrs Robert Carver (housewife)
1962 - Arthur Carver, parking attendant, 205 Victoria Street North. At same address: Dollie Ferguson.
1963 - Arthur Carver, janitor, 205 Victoria Street North. At same address: Dollie Ferguson, Gladys Lawrence,
1968 - Arthur Carver, retired, 205 Victoria Street North. At same address: Dolf Jacques (ret), Edra Laughlin (ret).
There is an ARTHUR CARVER who sails from Liverpool to Halifax, Nova Scotia aboard Empress Of Britain arriving 25th Feb 1919. Returning home after war?
Neil (Easby)