Cant speak to petroleum but with power if you can handle working nights cant beat the amount of time off you can get working shift work as an operator. And time off work equals more time sledding
Power (operator) is surface equipment and petroleum is typically downhole (underground/below wellhead). If you wanna work shift work, your career out in the field, easy on the body job and make good money go operator route.
If you wanna have options to work in the field or head office Petroleum is your choice. Main focus areas are Reservoir, Drilling & Completions and Production. If you choose the head office route you'll find your diploma is may not be enough and you may choose to get your engineering degree. Companies preference is to typically hire engineers (engineering degrees), so you may find your diploma limits your options.
In the plants, Operations is King. Power Eng is about Power generation in the form of Steam. Not all plants focus on the boilers, except power plant like Genesee.
PET, IET all take direction from Operations because they make the money by running the plant.
As a 2nd Class Power Engineer, I have been through the Plant Operations, Turnarounds, project work and ultimately launched my International career overseas for the last 15 years.
Power Engineering 5th through the 1st can be obtained with out going to school. Just need Boiler time and the SAIT Correspondence courses completed to write the ABSA exams. Going to SAIT Power Engineering Technology will only get you half of the 2nd Class ticket, the rest is by correspondence. The last half is the tough part and the 1st is even tougher.
Petroleum Engineering has to be done in school.