The launchpad says the package in question is GPL 3
(https://launchpad.net/ubuntuone-client)
Use this to download the source code:
bzr branch lp:ubuntuone-client
I'm pretty sure that all other packages in the Ubuntu One project
(https://launchpad.net/ubuntuone) are also free software, so it doesn't make
sense that it doesn't work in Trisquel.
Also, I don't think that just because Canonical is more lenient that they
would deal with proprietary software if it were feasible to do otherwise. I
can understand why they include software like Skype or Flash because the free
alternatives work nowhere near as well, but we're talking about products
Canonical themselves have made. If Canonical were okay with including
non-free software in their syncing service, it would have been more practical
to partner with a service like Dropbox as the basis.
