We share a similar potential predicament.

I'm in Elliot Lake, a 2.5 hour drive west of YSB and a good 6-7 hours from YYZ.
We usually drive to Sudbury and stay overnight before early am flights.

Wx problems can usually be predicted but all too often the early am AC flights from YSB to YYZ seem to be cancelled for no apparent reason, and switching to Porter is not an option as that means being "dumped" at YTZ!

You have in effect answered my question in that your onward AC flight reservations from YYZ are unaffected.

However, we're probably giving up on YSB and driving to YYZ because of the parking deals there. We stay at a hotel the night before a lengthy (25-28 days) overseas trip and the day of return and park indoors free! Nothing like this up here in the north.