IMHO, Canon are terrible for linux support. I am biased, I do have an old pixma ip4500, and I did have to purchase the turboprint drivers if only to print CD/DVD's.
Only just dumped TurboPrint in the last week. Reason, new Brother Printer which works just as good. Keeping the ip4500 until the ink stock runs out.
So this is in a PCLOS machine, Gimp 2.8.6 and Gutenprint 5.2.9 and a medium sized panorama.
http://i.imgur.com/75wNgrG.jpg best I can get is 600 dpi which to be fair is not that bad for this image.
but tweaking using adjust output is a bit hit-and-miss, no real clue as to the outcome.
http://i.imgur.com/xjEisUH.jpg A better bet. I would do some pre-processing with something like delabratory
http://i.imgur.com/dm9JmER.jpgI know you have a good camera (unlike me) have a look at partha's site for references, really easy to compile. Supports RAW (with a bit of luck), tiff's and jpegs.
edit: does not really answer your question about Gimp colour management, but you do not have a monitor profile set so what you get is nothing like what you see.
Have a browse round one of my favourite sites.
http://www.cambridgeincolour.com/maybe -
http://www.cambridgeincolour.com/tutori ... ration.htm