Hy there!
I have a problem to understand canonical links: I have a page on my website that gets in the url, into a parameter source, the site where the users was before, but only if he comes from adwords. Otherwise I don't have any parameter and I want to verify if there is or there isn't that parameter and send the right link with canonical. I realise that I am not very clear in my explain, but that is because I don't know exactly how to use the canonical link. If you can make me understand, please do. Thanks a lot!