If Airfare is the only issue then also consider about companion or child (if any) whether they can tolerate 16 hrs non-stop travel from Pakistan to Toronto. BD-PAK I think travel time will be 3.5 hour and it will not be matter even travel by parachute.
There is no doubt that this is the lowest fare. I have already gone through some user reviews for PAK-Toronto route in different forums. To be summarized, their comments are, 2 times spicy meal for 16 hrs journey, average delay time 2 hrs, seats are average with poor or no entertainment system but have enough leg space, toilets with/without washing liquids, aircraft overall quality is average, etc. Positive site is total time from BD-Toronto is relatively lower than other routes. Probably, it will starts from BD around 3 PM and will arrive in Toronto around 2 PM local time. Transition time in Pakistan is only about 3 hrs.
Finally, one has to decide route considering fare, Duration and comfort. Frequent air travelers can easily choose this route if consider fare and duration. I was expecting answer from someone from BD who used this route but it seems that none have use this route.