Yes, there are periods of the slow season in which AC subs the 788 in favour of the 789 to BNE (the 789s in turn replace 77Ws to destinations such as HKG). The 788 from YUL to Brisbane is uncommon, despite what this week's activity displays. 549 generally continues as 35, but there are no hard & fast rules, and if there were, we could always find exceptions.
I think the issue of bad weather at AC hub airports is a bit of a red herring. With 80 years of operation, AC should by now understand the seasonal challenges of operating in this country during winter, and draw their schedules accordingly.