Canada's constitution includes some very broad provisions -- most notably, section 7, which provides for the "right to life, liberty and security of the person" and has been applied to issues ranging from the abortion (Morgentaler) to private medical insurance (Chaoulli) to the operation of supervised drug injection sites (Insite) to the prohibition of penal sentences for absolute liability offences (Re B.C. Motor Vehicle Act) -- but they are limited by section 1 which states that these rights are "subject only to such reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society".
A very large number constitutional cases end up hinging on the words "demonstrably justified", which is why it looks like judges are making decisions based on what seems "fair": They are, quite literally, called upon to decide whether there are good reasons for laws or if the laws are arbitrary, broader than necessary to achieve their purpose, et cetera. As a result, it's necessary to look at external evidence to determine the constitutionality of laws, and a law which is constitutional today might be unconstitutional tomorrow.
Or as one lawyer I know put it: If Canada's constitution were a normal law, it would be ruled unconstitutional on the grounds of vagueness.