Farima Apa,
Turkish is the most reasonable airline for this route at this moment. Transit in Istambul is 5.5 hours not 8 hours. The rate is still very good. As i know till yesterday, it was 69,000/- per adult and 56000/- per child and 6000/- per infant. (All one way including tax and everything). They allow highest luggage of 69 + 8 kg per ticket. The timing is also very good. Depart from Dhaka at 9:30 pm and arrival in Istambul at 5:30 am. Again start from Islambul at 11:00 am and arrival Toronto at 3:30 pm (Toronto local time.) Transit will also be spent with taking breakfast and refreshing after whole night journey and again check-in for toronto flight. So ithink, it will not be problem. Considering all together, Turkish is preferable.
Ahsan