For Nikon I can use the free
ViewNX 2 to adjust the white balance for NEF raw files.
Is there an equivalent from Canon for CR2 files (also free)?
Canon bodies comes with Digital Photo Professional, Canon's RAW converter which has White Balance adjustments (as well as plenty of other settings as well). The downside is that it's not free, per-se. I'm pretty sure you need to have the original software disk that comes with your Canon body in order to use the updates which are provided on Canon's website. So there is no direct link to download a standalone version of DPP.
There are ways to work around Canon's silly restriction, but I believe it's outside the scope of this question (though google is your friend).
Ufraw, either the stand alone version or as a plugin to Gimp, will do the job nicely.