Canada does have a Constitution. It is primarily contained in the Constitution Act of 1867 and the Constitution Act of 1982 but includes a number of other documents as well. It isn’t as neat as the United States Constitution, but it is a written Constitution.
It also contains some ‘unwritten’ provisions that come from British Common Law (as does the UK, and most of the other Commonwealth Realms). Though ‘unwritten’ in the sense that they are not set down in any particular formal document, these are generally clearly understood and have been documented in analysis of Common Law.
We do have a Constitution, but it is not confined to a single document. It consists of several Acts of Parliament, English Common Law and court rulings.
Yes, we do have a constitution. The Charter of Rights and Freedoms is part of it: http://en.wikipedia.org/wiki/Constitution_of_Canada