There isn’t one!
I have a BJ F870 available to me, and it worked straight away with OSX Leopard, Snow Leopard removed that driver and didn’t replace it.
Apple had an updated set of canon drivers for download: Canon Printer Drivers for Mac OS X v10.6 2.1 [apple.com] – I am not sure if these will be a part of auto update or not, but it expanded my choice of canon drivers. Unfortunately still no F870.
I do not know if this exact printer exists outside of Japan as I was only able to find it referenced on the BJ driver page for Canon Japan [canon.jp].
I did get my printer working, seemingly normally by selecting the driver manually as a BJ F890 – a driver which came in the extra drivers download.
I wonder how many people were caught out when their printer drivers disappeared.
Another option which I didn’t try would be to grab the 10.5 driver from the Canon page and try to force it to install – per this trick: Install Canon printer drivers in Snow Leopard [macosxhints.com].