I think expanded advanced voting accommodates flexibility better. Some ridings are geographically large and not everyone can clear the single voting day. A single voting day might have worked better in days of yore with hubby working and a home maker at home. Some people are a lot more mobile in their employment. Others, like farmers or fishers, might find it hard to clear a day depending on the time of year.
Voting is a foundational act of a functioning democracy and, in Canada, Constitutionally protected. I think it is correct that the State do what it has to do to provide reasonable accommodation while at the same time ensuring its integrity.