It looks like AC are already planning for the elimination of the E90 fleet as this summer they're largely now relegated to high RASM short-haul routes.
YOW-YYZ are currently flown almost exclusively by E90 + a daily 767 (some A319/320 on occasions)
but looks like all flights have been scheduled to either A319 or A320 after the first week of September.
I suspect the majority of E90 will indeed be gone by September after the summer season.
actually I might be wrong,
E90 reappears on their booking site in the winter but of course it can be changed easily. :/