Note: This answer is obsolete. The bug was fixed on August 7, 2012, and can/should be fixed with the regular Update Manager updates. See this answer if you would like to install it manually.
This bug is special in two ways from a lot of other garden-variety bugs ;)
- It's a regression (when an update causes something that was working just fine earlier to stop working)
- It's "critical" importance (anything that causes most Canon printers to print out half-pages should!)
So, it will definitely show up in 12.04 updates soon, considering that it took 3 days to fix it for Quantal.
I strongly advise waiting for the above. In theory, you can install the Quantal debs, but CUPS is not a solitary package -- it has tons of dependencies which you'd also need to install manually. In short, this route can get VERY messy.
In the meanwhile, the more practical option is to downgrade to the previous CUPS version which works just fine. Do this with:
sudo apt-get install cups=1.5.2-9ubuntu1
To prevent upgrading it until a fixed version is released, hold it with:
sudo sh -c "echo cups hold | dpkg --set-selections"
and keep an eye on the bug report page. When a fix is available, you can install it and release the hold with:
sudo apt-get update && sudo apt-get install cups