This event determines the skaters who will go forward to Canadians in Saint John, New Brunswick in January.
The qualifying structure is explained here:
https://skatecanada.ca/athletes/qualifying-structure1/
18 singles, 15 dance, and 12 pairs qualify for nationals. For seniors, there aren't enough entries in dance or pairs to eliminate anyone, so everyone qualifies as far as I know.
In singles for senior men, Messing, Nguyen, Reynolds, Sadovsky, and Nadeau have byes via top 3 at last years nationals and/or having a senior grand prix. Gogolev has a bye for making junior grand prix final. So the top 12 from challenge (not including Nguyen and Reynolds who are/were entered) will qualify for nationals.
For senior women, Daleman, Austman, Chartrand, Pineault, and Mallet have byes via top 3 last year and/or senior grand prix assignment. That means top 13 from challenge (not including Austman and Pineault who are entered) will qualify for nationals.