On my canon i950 printer, a green line prints out at the whole bottom edge of the picture when it is printed. I have done the deep cleaning and it still comes out like this.

Try this then.
OK, Canon will hate me for posting this.

1. Remove ink cartridges
2. Remove print head
3. go to sink or tub (stainless steel, not plastic type), pick up a roll of paper towel on the way.
4. Fold several layers of paper towel and place on flat surface.
5. Run hot water until HOT!
6. Turn hot water back to a dribble.
7. Run the dribbling hot water through print head, be careful not to wet the gold contacts.
8.When water running through print head is clear, place print head on paper towel.
9. Repeat number 7 and 8 until no colour shows on paper towel.
10. Gently DAB print head (DO NOT WIPE) inside and out with dry paper towel until dry.
11. I normally replace print head after drying, but you may wish to let it air dry overnight.
12. Replace print head in printer and install cartridges
13. Start printing.

I do this to all 4 of my Canon printers every 6 months or so.

If any colour fails to print after this process it means your print head probably needs replacing.