Did you do any internet search before asking here? I searched "Canon Pixma MX870 linux" and found these links:
http://support-sg.canon-asia.com/contents/SG/EN/0100272302.html
https://www.linuxquestions.org/hcl/showproduct.php/product/4447
https://bbs.archlinux.org/viewtopic.php?id=143349
Reading those it looks like a specific printer driver must be installed before CUPS setup. Not every printer needs that, so perhaps that is why it is not mentioned in the wiki page you read.