Thanks for your reply.
I located the same 1901 and 1911 censuses you have shown, plus those for 1881 and 1891, which I’m sure are those for “my” John Beer, butcher + Susannah. These consistently show Susannah as being born in Ireland, not in Hope county as on the potential marriage record you found for Susannah M Austin to James Bye – and also an 1891 census for James Bye (b. ~1838, England) and Susan M Bye (b. ~1845, Ontario). I therefore don't think this is the correct Susannah Austin.
The writing on Susannah’s death record is very faded and I couldn’t decipher anything for her mother’s name, although her father’s name is possibly James. I couldn’t find any marriage records in Ontario for John Beer to anyone named Susannah. There is one for another John Samuel Beer to Elizabeth Guy on 29 Dec 1898 in Toronto – but the parents (George Beer and Mercy Ellen Blake – “my” John Samuel Beer’s parents were John Barrett Beer and Sarah Priscilla Couch), occupation (machinist, rather than butcher) and place of birth (London, rather than Devon) are incorrect, so that is definitely for someone else.
Incidentally, the 1901 Census for “my” John Beer shows an emigration date of 1870, but I think it was somewhere between 1871 and 1877, as he is still shown on the 1871 Census in England and everything on that is compatible with the 1841/1851/1861 England censuses plus everything else I know about him. His oldest daughter with Susannah was Sarah Elizabeth Beer, who was born in Wentworth on 19 Feb 1878. I have found a Passport Application on 29 Apr 1874 for “J Beer”, which is a possibility, but it is on a register and no other information is provided to indicate whether it might be correct.
As later records come on-line for Ontario, I'm hoping it may be possible to find out what happened to the 7 children.