If you are searching for a legitimate, standalone APK file (an Android app package) for Marvel vs. Capcom 2 that you can simply install and play, it does not exist.
Capcom has never released an official port of Marvel vs. Capcom 2 on the Google Play Store or the Apple App Store. The last official mobile release for this game was on iOS way back in 2012, which was eventually delisted and is no longer compatible with modern devices. If you are searching for a legitimate, standalone