I've just run into the same complication as you did. My Pixma MP780 no longer works since I upgraded to Lion 10.7.2. Canon USA doesn't list any drivers available.
Were you ever able to resolve the issue? I would greatly appreciate any advice/insight you might have on the matter.
I have the same problem! I upgraded software and the Canon MX780 printer just went away. Print & scan has the Canon MX870 series put only the scan options. However, I can still print from a networked laptop. Just like I always could. Thinking of importing the laptop DMG and trying to install it. Canon site has only a scanner driver.
Apple support site tells me that Canon printer driver for MX870 is"
Canon MX870 series 10.51.2.0 P
Like I said I can print from a networked laptop.