At UBC here in Vancouver, most fraternities and sororities have an annual invitation-only themed pledge party, usually in December, January or February (from what I've heard). Ours is typically Jan or Feb. As for mixers, we call them exchanges here, and it involves the entire chapter & not just the new members.
At most Canadian schools out west, we DON'T use the terms freshman, sophomore, junior & senior ... we use 1st year, 2nd year, 3rd year, 4th year, etc ... do any of your schools do this?? For high school, we refer to one's grades (eg. grade 8, 9, 10, 11, 12) instead of labelling grade 9's as freshman. Most high schools out here in the west begin at grade 8 anyways. It is only out east (Ontario) that the term 'frosh' is used at universities.
just thought I'd share
Jen - alumna
AGD - Delta Zeta '97
University of British Columbia