Cloaking is a search engine optimization technique in which the content presented to the search engine spider is different from that presented to the user.
Black hat SEO is a disapproved practice that increases website's ranking in a SERP. This is not a good seo technique because it can cause the site for being banned from the search engine.
Black hat SEO refers to the use of forceful SEO techniques that focus only on search engines and not a human audience, and usually does not obey search engines rules.
The rel=canonical tag passes the same amount of link juice as a 301 redirection and often takes much less development time to implement. This tag is part of the HTML inserted into head of a web page.