CPAC is a Canadian cable channel, which broadcasts proceedings of the House of Commons, Parliamentary and Senate meetings, and everything else to do with Canadian politics.
Waaay back in High School I was particularly good at political science, so much so that one of my classmates remarked out loud in class, "Jeez man, what do you do in your free time, just watch cpac?!?" (I didn't for the record), and from that day on, classmates started calling me, "cpac" and it just kind of stuck.
As for the 54 at the end, it was a random number thrown on there when signing up for my very first hotmail email account back in the day, and I've kind of just used the combination ever since!
This is a hilarious story and nickname to pick up in school. We were uncultured philistines and just called each other "gay" a lot lol.