I wouldn't say that service varies on different aircraft. Whether you are on a 319 or a 340 trans-con, the service is comparable. If anything, I would say it would be better on a 319, because there are only 16 pax.

AC domestic J is fully comparable with UA F--better in many respects. In fact, UA sell it as F on the codeshares.

AC international J blows other J class products out of the water. The only thing it is really missing is a full-flat bed (like BA), and emPower on all equipment (presently only on the 330's and a few 340's).