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There is no such thing as a "Schengen Airport Transit Visa". What you will need for this itinerary is a regular multi entry Schengen Visa.
The reason that you need this is that you are taking an internal Schengen flight. For the purpose of immigration control the whole of Schengen can be considered as if it was one country, and an internal Schengen flight is like a domestic flight in the US or Canada. There is no passport control when flying within the Schengen area.
So you will need to pass passport control and enter the Schengen area to be able to take your flight to Vienna. Then in Vienna you will pass passport control again, now leaving the Schengen area.
It does not matter that you will only spend a few hours within Europe. You will need this Schengen visa, and this for both ways. Hence get a multi entry one.
If you are flying a route that would only touch one airport within the Schengen area, so without an internal flight, then you do not need a Schengen visa. You will be able to stay in the airside non-Schengen transit zone.
But you might still need an Airport Transit Visa (issued by the country involved) under certain circumstances. The rules differ by country, but usually Indian nationals with valid Canadian or US residence permits would not need a transit visa when transitting through Europe on their way between North America and India. But do check.