Actually, there has often - perhaps even usually - been a debate in English.
Not true, the only other English electoral debate in Quebec was in 1985 between Robert Bourassa and Pierre-Marc Johnson and it was only broadcast on CJAD and never televised. This is the second ever english debate and the first ever to be on TV. Ironically we have Jean-François Lisée to thank for this debate, he was the first person to suggest it and the other leaders agreed.