I was in the US when Paul Martin was kicked down to a minority. I voted in that election and I didn't show my face when I voted.
I sent in a photocopy of my driver's licence and my passport and I was mailed back an absentee ballot.
So, to create a "someone has to see your face on voting day" rule would likely disenfranchise the huge number of Canadians that live abroad but are actively involved in Canadian society.
Let's be honest, most people DON'T like the idea of women in our society covering their faces. However, to express this concern using voting laws is problematic.