Tuesday/Wednesday flights with returns on Tuesday/Wednesday are $355CDN on non-stop Air Canada flights from January through 'til mid-June.
Act fast as these prices will disappear! The flights need to be booked in US$--for $281USD, which after forex fees comes out to around $355CDN. Through Air Canada and CDN websites, it costs $16 more, so your choice.
Priceline is a great way to go, as you have until 11:29ET the next business day to cancel by, so if you book now, you'll have until 11:29ET to go back on the Priceline website to cancel your tickets if you wish to book now and think about it after.
See the availability on Google Flights here. Click on a date to open up the calendar to see the prices for departures and returns. Prices to San Francisco direct are usually not this cheap, as you'll see when you open up the calendar.