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HI

This is from Air Canada:

Air Canada, Air Canada Rouge and Air Canada Express are approved air carriers participating in the Canadian government's Transit Without Visa (TWOV) program, and China Transit Program (CTP). This participation allows our customers who are citizens of certain Asian countries and who are transiting through Vancouver Airport, Calgary Airport or Toronto-Pearson Airport (Terminal 1 only) to travel to or from the United States without obtaining a Canadian temporary resident visa under certain specific conditions.

1. Go back read post #5 it outlines the conditions for TROV. The OP is from India, needs a Transit visa.
 
OP has a one time entry visa for him to come Canada for landing, since he would not have to clear Canadian immigration on his way to US therefore the validity of that visa should be preserved. Could he not use that visa to enter Canada from the US?