James, the first two answers to your question are valid: AC generally offers a better hard product (than non-Polaris only) and easier connections than UA, but the UA regular business class product is far from awful. Note the "not even close" comment included a configuration on a plane that UA doesn't even fly to Australia. My own experience on AC 33/34 has been hit & miss, and the term 'lie-flat seats' at Air Canada takes on an entirely new meaning if you score a deflated cushion.
Agree with StuMcIlwain above that if you can find UA space, grab it. A variable I'd consider with UA is the YYZ-->US west coast leg, as it may not offer superior connections like in YVR, nor will it be a lie-flat seat, unless you manage to get AC Signature to LAX/SFO. For such a short leg, that's not generally a factor, although it may be appreciated on the eastbound leg following a long TPAC crossing.
Best of luck; your father should be very comfortable on either airline.
Last edited by tcook052; Sep 16, 2018 at 9:38 pm
Reason: personal invective