Flights ought be bought now for lower prices, but how to forecast the best days? The quotes beneath contradict: the 1st 2 recommend mid to late September, but the last one the 1st week of Oct.
National Post dated Sep 8 2015:
Tourism Quebec’s Claudette Lacombe says bursts of red, yellow and orange will soon begin to appear as leaves change colours with the approach of fall.
“The peak is from the end of September up to mid-October, but if visitors don’t want to miss the colours they should come in mid-September until the end of September,” she said in a recent interview.
[...] Anyone planning a fall colour tour in the province should check the bilingual website Quebecoriginal.com starting in mid-September. [I'm aware of this website.]
User 'rickb' from Tripadvisor. Feb 6 2013:
Back to the fall colors. October is too late for peak season in Charlevoix, hence my suggestion of moving to the Mont-Tremblant area where it will be in full bloom.
User 'Jean-Simon C' from Tripadvisor. Feb 3 2013:
Perfect timing, the color peak is around the end of september/beginning october in this region.