Hi,
You can either prepare/email all the documents, they then print and submit it in person to VFS Mumbai..... OR you can apply online and they can submit their passports, in person, at VFS Mumbai for TRV stamping.
They have to fill separate forms.
It's best if your parents show they have the finances for the visit..... typically CAD 1000 per person per week + airfare. Submit 6 months' bank statements + FDs, shares, mutual funds, PPF, LIC, etc etc + 2 years ITRs
Proofs of relationship: Their marriage certificate/your birth certificate/their passports stating each other as spouse
Sample invitation letter: http://www.cic.gc.ca/english/visit/letter.asp Also Google/check this forum
Other points:
How long do your parents want to visit?
Prepare an approx day-by-day tourist type of itinerary + prove they have strong reasons to return (property ownership, family that lives with them, a must return by XX date + previous travel history will help, etc) + buy refundable overseas travel medical insurance (though this is not mandatory)
Cheers
