yes, pre-clearance in YVR, so you’ll do immigration/customs in YVR. If you don’t have GE, definitely arrive at YVR 2 hours prior for those for formalities.

If youre on a night flight out out of SFO, I’d presume you are on an afternoon/early evening flight out of YVR. Don’t forget delays can build through the day (ie, delays in the morning continue through an aircraft’s schedule all day), and so from that perspective, they can get worse later in the day. Keep that in mind. There are situations/airports I would book a 45 minute connection in if traveling alone - through personally, I generally wouldn’t at SFO.

Also, just take note of who is operating your flight out of YVR so you know where to check in - UA codeshares on the AC YVR-SFO flights.