Regarding GPA, from my understanding, UBC does not consider the average of the courses that you're taking or the difficulty of your major when they look at your GPA. As a result, I would recommend taking courses that you might enjoy while also looking at UBC pair to view previous averages for the courses so that you have a better chance at succeeding.
Regarding volunteering, I only volunteered at a hospital since last August but took on a volunteer opportunity at a more isolated hospital that would enable me to have more unique experiences to talk about. For example, i volunteered in the psychiatric ward at a hospital, which exposed me to a new demographic and provided me with a solid foundation to discuss in my personal profile. This is better suited to the type of application versus volunteering as a way finder, which may have limited information to discuss. All in all, try to take on opportunities that are unique and allow you to stand out.
Regarding the Casper exam, from my understanding, the Casper exams are written every year and disregard past exams. Here is a link to the Casper website page that discusses what evaluators look for in a strong exam. Top 12 Tips for an Oustanding CASPer Performance | CASPer Test
To those who were accepted into UBC for this year, congratulations and to those who were not accepted, I wish you the best moving forward in whatever path you take.