What is the highest package in mechanical engineering in IIT Kanpur?

If you are looking for monetary statistics, you are in the wrong place. IIT Kanpur does not release branch-wise placement statistics.

Packages hardly depend on the branch. Your performance throughout the 4 years and your small and big achievements determine the kind of packages you are offered.

Infact, even a CS student shouldn’t expect great packages if his grades are below average and he has not worked hard and gained knowledge and skills. Even Sundar Puchar was a metallurgy BTech student but today is the CEO of Google. 

The conclusion is that your branch does not determine your package, your grades do.