If you're not paying attention, yes. I checked flights on Kayak from SF to Vancouver and a lot of the results look like this: Tue, May 2 Air Canada logo 10:4

If you're not paying attention, yes. I checked flights on Kayak from SF to Vancouver and a lot of the results look like this: Tue, May 2 Air Canada logo 10:45a – 1:01p Air Canada• Operated by United 2h 16m SFO – YVR nonstop Flight details That's because United and Air Canada "codeshare", meaning you can book with United or Air Canada but that flight is on a United plane. Of course, it goes the other way: you can book an Air Canada plane but use a United flight number. https://www.united.com/CMS/en-US/Marketing/CustComm/Promotions/Pages/AirlinePartners.aspx https://www.united.com/CMS/en-US/Marketing/CustComm/Promotio... https://www.kayak.com/flights/SFO-YVR/2017-05-02/2017-05-07?fs=specificleg=SFOYVR1493719200000AC51151;providers=-AA https://www.kayak.com/flights/SFO-YVR/2017-05-02/2017-05-07?...