One thing that makes a big difference between fair use and fair dealing is that the courts in the U.S. have said that there are no bright-line rules, so you cannot come up with guidelines the way the education sector has done here and say you can copy up to 10%, a chapter, etc., and be blessed to go ahead and roll that out across the country, as has been done in Canada. In the U.S. that is not possible. There are no bright-line rules at all.
Another element that is quite different between the U.S. and Canada is that in the U.S., if there is an impact on the market for the work, that is one of the most important aspects in looking at fairness, and the availability of a licence tends to trump the fairness of the use in the U.S. It is not so clear in Canada how that works.