Hi Nisha,
If this is your first long flight, forget abt saving money in Air India.
You will enjoy Jet or BA..With Jet yes you will pay a few thousands more than AI but it is worth it..always avoid flying inside india which can tire you..
cos chennai security check is more than enough...they are very strict and long line ups for immigration...with Jet there is only 2 hours transit in brussels, and that will fly once u clear security in belgium. All you have to do is change the flight, you will get on to the Delhi-Brussels-Toronto flight in brussles..its stress free and you will love it...
Total flying time including transit would be around 21 hours