I believe the longest current nonstop domestic flight in Canada is Westjet flight WS169, a 737-700 from YYT
(St. John's, Newfoundland) to YYC
(2695 mi/2342 nm, elapsed time 6:09).
The longest direct flights (same flight with one or more intermediate stops) are probably 2 daily AC
A320s (AC1175 and AC109) that operate YHZ
(2887 mi/2509 nm, elapsed time 8 hrs.)
also has a 1 stop YHZ
737-700 which is a little shorter than via YYZ
(2798 nm/2432 nm) and elapsed time all the way of 7:30.
has a sllightly longer 1-stop, also 73G, WS229 YHZ
(Comox, British Columbia, a small community and air force base on Vancouver Island about 85 miles north of YVR
). That's 2823 mi/2453 nm) and elapsed time of 7:45.