No, you don't need transit visa In UK, as you will be holding valid Canadian study visa (and also US visitor visa, which you are not intending to use) and have connecting flight in 6 hours or so..Also you can confirm with the airlines you are planning to fly.
I would call makemytrip customer care to window shopping their flights and have my questions answered.
Just found this from UK visa website:
"What’s your nationality as shown on your passport or travel document? India
What are you coming to the UK to do? Transit (on your way to somewhere else)
Where are you travelling to? Somewhere else
Will you pass through UK border control? No
You’ll need a visa to pass through the UK in transit (unless you’re exempt)
Exemptions
You don’t need a visa if you have one of the following:
- a visa for Canada, New Zealand, Australia or the USA (this can be used for travel to any country)
- a residence permit issued by Australia or New Zealand
- a common format residence permit issued by an European Economic Area (EEA) country or Switzerland
- a resident permit issued by Canada after 28 June 2002
- a uniform format category D visa for entry into a country in the European Economic Area (EEA) or Switzerland
- an Irish biometric visa (marked ‘BC’ or ‘BC BIVS’ in the ‘Remarks’ section)
- a Schengen Approved Destination Scheme (ADS) group tourism visa where the holder is travelling to the Schengen country that issued the visa
- a flight ticket from the Schengen area, if you can prove that you entered the Schengen area in the previous 30 days on the basis of a valid Schengen ADS visa
- a valid USA I-551 Temporary Immigrant visa issued by the USA (a wet-ink stamp version will not be accepted)
- a valid USA permanent residence card issued by the USA on or after 21 April 1998
- an expired USA I-551 Permanent Residence card issued by the USA on or after 21 April 1998, with a valid I-797 letter authorising extension
- a valid standalone US Immigration Form 155A/155B issued by the USA (attached to a sealed brown envelope)
All visas and residence permits must be valid."
Hope this helps, Cheers.!!