Although AC does not have E+ seating, its standard Y pitch is 32". Also, the first several rows are considered "premium" and first seating assignments do go to elites and full fare Ys. On day of flight, this allocation is dropped and gate agents can seat anyone anywhere, and usually do. AC is pretty miserable at providing a decent accommodation for its elites in the back cabin, claiming their software cannot block the middle seat, etc. They only say these seats will be kept empty [except when couples, families are travelling together] until the window and aisle seats have been allocated. Then they infill.

AC elites have complained for years about this situation, but the airline has done nothing to make the situation of seating any better. Such a simple way to make us happy!

As noted, UA elites cannot upgrade on AC metal codeshares, nor can AC elites upgrade on UA metal codeshares. AC does sell upgrades on some of its transborder routes, but these can only be used from full Y fares, and certainly not from V.