Sam makes the excellent point that it is is unlikely that legislation that codifies a more liberal approach to fair dealing or has the effect of "relaxing the categories", would be subject to a trade-law challenge. Sam is an American trained lawyer and has expertise in both Canadian and American copyright law.
Sam suggests that:
The Act's fair dealing provisions should be amended to correspond with the values stated by the Supreme Court of Canada in CCH v Law Society of Upper Canada  1 S.C.R. 339. This could be accomplished simply by adding the words "such as" to the existing listing of categories and by incorporating the six fair dealing criteria adopted by the court into the Act.The idea that reasonable steps in this direction would violate the three step test requirement of Berne, as suggested by Messrs. Sookman and Glover, is simply bizarre. Nobody has ever seriously suggested that Section 107 of the US Copyright Act contravenes Berne. Obviously, the US Government doesn't think so. For example, this provision explicitly states that that multiple copies for classroom use can be fair use. It also explicitly leaves the list of examples of fair use open, which has, for example, enabled the US Supreme Court to rule that parody can be fair use.
If Canada does what Sam suggests, the USA would look rather silly if it were to launch a trade challenge based on the Berne Convention and the three step test. It's a safe bet that there would be no such challenge.