Léonie,
Thanks for all of your help narrowing this down.
I'm still not able to import so I'll capture some more specifics here, for the community:
- Canon VIXIA HF R600 video camera set to movie format "AVCHD" and video quality "60P"
- OS X Yosemite Version 10.10.4
- Photos Version 1.0.1 (215.65.0)
I unsuccessfully dragged and dropped the following onto the Photos icon in the Dock:
- file:///Volumes/CANON/PRIVATE/
- file:///Volumes/CANON/PRIVATE/AVCHD/
- file:///Volumes/CANON/PRIVATE/AVCHD/BDMV/
- file:///Volumes/CANON/PRIVATE/AVCHD/BDMV/STREAM/
- file:///Volumes/CANON/PRIVATE/AVCHD/BDMV/STREAM/00000.MTS
Each time Photos came to the foreground and presented the following:

Since you were able to verify that it's possible to import AVCHD video into Photos for OS X and have it upload to iCloud Photo Library, I'm guessing that the specific AVCHD file format that my camera produces is not acceptable, or that my software is a different version. I see that I can install OS X 10.10.5, so I'll try that next.
Thanks again for all of your help. And I don't expect that you'll go out and buy the same video camera to help me further. 😉
Thanks,
Todd