Unfortunately, photoshop elements 11 can only use up to camera raw 7.4 for the camera raw plugin.
(in the photoshop elements 11 editor; Adobe Photoshop Elements Editor>About Plug-In and click on the words Camera Raw to find the version you have)
(Help>Updates in the pse 11 editor to check for updates)
You can use the DNG converter 8.6 to convert your canon 70d files to dng copies, which pse 11 should then open.
If you have mac os x 10.6.8 snow leopard then you would need to use dng converter 8.3
dng converter 8.6:
Adobe - Adobe Camera Raw and DNG Converter : For Macintosh : Adobe DNG Converter 8.6
dng converter 8.3:
Adobe - Adobe Camera Raw and DNG Converter : For Macintosh : Adobe DNG Converter 8.3
How to use the dng converter:
Camera Raw: How to use Adobe DNG Converter - YouTube
You could also upgrade to photoshop elements 12 or look at adobe lightroom 5.6 to avoid using the dng converter