Air Canada flights from San Francisco to Copenhagen via Toronto are priced as low as $366-$396 round trip through Momondo.com for travel in October and November. These can also be booked through Air Canada or United.com for higher prices. Low fares are available August to December 2018.
To quickly find $366 fares, search Google Flights SFO to CPH for $422 round trip tickets on Star Alliance. Tickets priced at $422 and $452 on Google Flights and United.com priced at $366 and $396 on Momondo.com searches for these dates.
August also has some United transatlantic flights around $500 round trip. United flights in August at $510 on Google Flights priced at $497 on Momondo.com.
Momondo.com TravelMerry OTA link for Air Canada flights marketed as UA codeshare.
United Airlines San Francisco SFO – Toronto YYZ – Copenhagen CPH – YYZ – CPH
$396.01 round trip Mon Sep 17 – Fri Sep 28 ($452 on Google Flights)