Originally Posted by
hikouki
The advantage of the AC return flight is that connecting time is only 2-3 hours, but via UA it will be 4-6 hours, I guess to account for CBP processing (I do have Nexus).
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Have flown both to Europe from SFO several times. I would rate AC Business class better than UA, but the Lounge comparison goes to Polaris.
The shorter layover is always better. Remember you will clear US Immigration and Customs at YYZ.