Even though the files from your new 7DII are in the .cr2 format, the data in a raw file is always sensor specific. That is, each different sensor design must be demosaiced/converted differently to get the same standardized results.

Lr 3 is a while back. The latest version of Adobe Camera Raw (which is used by Lr to demosaic raw files) that is compatible with Lr 3 was released a long time before the sensor in the Canon 7DII was developed. It is no surprise that Lr 3 can't handle the raw files from your new camera. Since Adobe has chosen to not support newer cameras with older versions of ACR/Lr, if you wish to work with the .cr2 files created by your 7DII you have a few options:

• Update your version of Lightroom and Adobe Camera Raw to versions that can support the Canon EOS 7D Mark II.
• Use Canon's own Digital Photo Professional supplied with every Canon DSLR. Updates and even new versions such as the recently released version 4, are always free for owners of Canon EOS cameras.
• Convert the /cr2 files from your 7DII to the DNG format and edit them with Lr 3. Be aware that some information in the .cr2 file is discarded when converted to .dng. That information may or may not be important to you.