My basic checklist:

1. Who required the records to be created?
2. How long does that agency hold them?
3. Which records survive?
4. When records are past their keep date, are they turned over to an archive? If so, which one?
5. What collections are available online?
6. What information can you expect to find in the collection?

For background information on the history of elections in Canada see: Elections Canada (answering point #1)

For what collections survive: Library and Archives Canada's Genealogy and Family History Page on Voter Lists. Here's the catalog for the microfilm numbers for 1957.

Note also they say:

If you are looking for someone who lived in a city, search city directories instead of voters lists because the names of individuals are listed alphabetically.

The Toronto Public Library's Guide to Ontario Genealogy has a link to city directories at the Internet Archive.

Ancestry.ca has 1957 and it has been indexed:

Ancestry.com. Canada, Voters Lists, 1935-1980 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2012. Original data: Voters Lists, Federal Elections, 1935–1980. R1003-6-3-E (RG113-B). Library and Archives Canada, Ottawa, Ontario, Canada.

This blog post gives an overview of what you can expect to find: Why Canadian Voter's Lists Can Further Your Research

The FamilySearch wiki's list of Ontario records has a link back to the collection on Ancestry. I checked World Vital Records, but I didn't see any voter rolls for Ontario in their Census and Voter List catalog. It's not as easy to see what FindMyPast holds, but my very quick search seemed to indicate that the only Canadian electoral rolls they have are from 1952; without logging in, I couldn't see what provinces were covered.

My basic checklist:

1. Who required the records to be created?
2. How long does that agency hold them?
3. Which records survive?
4. When records are past their keep date, are they turned over to an archive? If so, which one?
5. What collections are available online?
6. What information can you expect to find in the collection?

For background information on the history of elections in Canada see: Elections Canada (answering point #1)

For what collections survive: Library and Archives Canada's Genealogy and Family History Page on Voter Lists. Here's the catalog for the microfilm numbers for 1957.

Note also they say:

If you are looking for someone who lived in a city, search city directories instead of voters lists because the names of individuals are listed alphabetically.

The Toronto Public Library's Guide to Ontario Genealogy has a link to city directories at the Internet Archive.

But back to voter rolls. Ancestry.ca has 1957 and it has been indexed:

Ancestry.com. Canada, Voters Lists, 1935-1980 [database on-line]. Provo, UT, USA: Ancestry.com Operations, Inc., 2012. Original data: Voters Lists, Federal Elections, 1935–1980. R1003-6-3-E (RG113-B). Library and Archives Canada, Ottawa, Ontario, Canada.

This blog post gives an overview of what you can expect to find: Why Canadian Voter's Lists Can Further Your Research

The FamilySearch wiki's list of Ontario records has a link back to the collection on Ancestry. I checked World Vital Records, but I didn't see any voter rolls for Ontario in their Census and Voter List catalog. It's not as easy to see what FindMyPast holds, but my very quick search seemed to indicate that the only Canadian electoral rolls they have are from 1952; without logging in, I couldn't see what provinces were covered.

Unfortunately, the Canadian Voter Lists are not part of the New Year's package of free collections that are searchable this weekend. The Toronto Public Library has some voter lists that can be viewed in-branch at the North York Central Library, but their collection doesn't cover 1957:

Ontario voters’ lists (incomplete 1847 – 1954 for various townships)

So the only thing I've been able to find online so far is the one digitized collection on Ancestry.

One good way of keeping up with what new collections are coming online is the online magazine Genealogy In Time -- here is their list for Most Recent Genealogy Collections in Canada.