If a person is missing from the census there could be several explanations besides them not being home. They could be mis-indexed under names that would not be obvious or they could have moved before enumeration took place in their area to an area where it had already been completed.
Check the Toronto City directories for 1911-1912 to get the address where they lived. Then use that address to locate who was enumerated there in the 1911 census.
It's also possible they were enumerated as single or they were living in someone else's household and were mis-indexed under that surname - check their relatives or do a search without surnames.