Toronto to Singapore - $674 RT (September 2018-June 2019)
Flights from Toronto to Singapore are available for $674 RT (flights are available from September 2018 through June 2019. I believe they were available earlier in the year as well, but don't see an active thread about it. Very easy to find these Air Canada/United combinations on Google Flights. Note that even if the price says it's more than $674 (i.e. ~$800), when you click through to the booking site, it seems to show the $674 price.
An example:
https://www.google.ca/flights#flt=YYZ.S ... .CAD.67366
An example:
https://www.google.ca/flights#flt=YYZ.S ... .CAD.67366