Most online TA will not be able to price mix class trip. Since BR does not provide PE intra-asia, online TA will not find anything.
If you insist doing it online, fly CX like someone suggested above or buy the YVR to YYZ ticket separately which likely to cost more.
Or try book a ticket for EVA in all Y from online TA, then call the online TA to change your booking to PE. If they said no, call EVA. If all fail, refund your ticket in 24 hours for no penalty.