I have a valid multiple entry schengen business visa issued by the German embassy for a duration of 1 year. I was supposed to travel at the beginning of May 2019 to Germany and use this visa but unfortunately my business trip got cancelled. Therefore, I have not used this visa so far. I wanted to know if I can use this visa for tourism and now can I enter Austria through this visa as it is valid for a year and is multiple entry visa for all schengen states ?
If you had used your visa for the purpose you applied for, it would be allowed to further use it for other trips even when those have a different purpose.
But as you have not used your visa the officer that admits you will have to trust that your reasons for applying and not using the visa are genuine. Some officers do, others will suspect fraud and block you from entering or even ban you.
As you did get the visa before it will likely be easy to get a new, tourist, visa. It will cost but it will give peace of mind. And not being allowed in will cost more.