The all in one Canon question is easy.
The Mp750,760, and 780 are all based on the ip4000 printer engine and hence are non-chipped.
The Mp750 adds a medium quality flatbed scanner to the mix so you get print, copy, scan.
The MP760 adds a higher quality scanner to the the mix good enough to do a decent job with 35mm slides. Again you get print, copy, scan.
The MP780 uses the same basic scanner as the MP750 but adds a fax to the mix. So you get print, copy, scan, and fax. Plus an ADF.
For what its worth, I don't see many MP750&760's anymore for street sale or ebay.----but the MP780 is still readily available retail. Yesterdays paper had the brand new MP780 on sale for $200. cash and carry at Staples. Its a very good printer well worth the money. I happen to have its previous generation counterpart, the MP730. It also is a very good all in one printer.
But my advise is and remains----get those non chipped Canons while they last. The supply is drying up fast.-----and boycott the chipped Canons until some way is found to defeat the rip off chip.-------and it sure does not mean go to HP or Lexmark----they are far worse than a chipped Canon.