Which international business class is better, United or Air Canada?

What's better if I was only able to fly on United Business Class LAX-SYD or Air Canada Buziness Class Vancouver to Sydney, in January 2015?

It would be good to know your origin?

AC business is far better, IMHO.  Even though UA will be a 777, AC has a better product, most notably the seat and in-flight meals + snack service.  UA seats are often lumpy/rutted, and you can be stuck in an unfortunate situation wherein you have a neighbour, whereas AC has a herringbone layout giving each JC pax unfettered access to the aisle and a blissful lack of direct neighbour PAX.

Lastly, if you're originating in Canada and not the US, flying AC will save you from US customs (and suffering LAX).

AC without a doubt! United really need to up their game internationally 2-4-2 layout! BA I forgive you and the meals are not that good either definitely AC