A controversial secularism law in Quebec is heading to Canada's Supreme Court - but the outcome will impact much more than religious expression in Canada, legal experts say. The case has the potential to test national unity and the balance between courts and elected officials. "This case is probably going to be the most important constitutional case in a generation," said Christine Van Geyn, executive director at the Canadian Constitution Foundation. At the heart of the case is Bill 21, which bars civil servants like judges, police officers and teachers from wearing religious symbols at work. It was passed in 2019, by the governing Coalition Avenir Quebec (CAQ). But to withstand legal challenges, legislators employed a unique Canadian invention, the controversial "notwithstanding clause". That legal loophole allows governments to override certain constitutional rights, including freedom of religion and equality rights.…