will my Canon pixma MP950 work with mountain lion for scanning?

The article you attached has the answer.

The article lists your printer under "Software Available", but it only has a "P" after it, meaning there is printer but no scanner software available. The article also lists Canon's website, which is where you will need to go for support.

There is no ICA driver available from Apple, which means you cannot scan using the included Image Capture or Preview applications. And checking the Canon USA web site, they have no drivers for this model for 10.8. So it would appear that the answer is no to scanning on 10.8

Your post lists an impossible pairing:

It says you have a Power Mac G5 and Mountain Lion. The Power Mac G5 cannot possibly run Mountain Lion. See: http://support.apple.com/kb/HT5444

I use Image Capture to scan documents on my MP950 with no problems under Mountain Lion. So I would give it a try, if I were you.