I have no relationship with Canon other than as a fairly satisfied user of their products. Canon do not pay me in any way, Canon do not support this site in any way, Canon do not pay for advertising here, Canon do not give me equipment. Similarly I'm not paid or supported in any way by any of Canon's business partners. In fact this site is not sponsored by any manufacturer and I'm not paid by anyone to write anything here.
The reason I write about Canon and often recommed their cameras and lenses is that I try to write what I know about and use. I could easily write anout Nikon, but it would be mostly 3rd hand information. I don't shoot with any Nikon cameras myself so I can't really write much about them. I can (and do) comment on their new cameras, but that's information based on technical specs rather than actual field ouse. When I write in detail about a Canon camera or lens, most often I've actually used it and so I think I can provide accurate information. I've also been using the Canon EOS system since the mid 1980s, so I think I have a pretty good backround in it and can offer some perspective on it. If I didn't think Canon gear was good, I'd have changed systems long ago!
Canon have occasionally loaned me equipment to review (digicams, printers), but so have Tamron, HP and a few other companies. I've requested items for review from other sources, but they have not been forthcoming. I'd be more than happy, for example, to review Sigma lenses, but despite several requests, they have not offered to loan me any of their lenses for review, so I haven't reviewed any Sigma lenses.