It used to be that the lowest fare would put you into J on the regional sector when the flight was operated by a 747 or A330 but now they only do it if you purchase the next highest fare and the fare difference is usually about $ 400 - $ 500.

CI is doing something strange with their PE fares. For example if I book YVR - TPE - SIN in the lowest fare class, about CAN$ 1,500, I get PE for the YVR - TPE sector and Y for the TPE - SIN sector which for the dates I am planning to travel are all operated by an A350.
When I choose the next higher fare which is an additonal $ 450 I get YVR-TPE in PE and TPE - SIN in J.
There seems to be no option to be put on all flights into PE.