As Ontario's election campaign kicks off, experts say the fight is on between the provincial New Democrats and Liberals to stake out their place as the main rival to Progressive Conservative Leader Doug Ford.

Both NDP Leader Marit Stiles and Liberal Leader Bonnie Crombie have come out of the gate trying to strike contrasts with each other on style and substance, and have already exchanged verbal barbs. Experts says it's all part of the so-called "progressive primary", the fight between Ontario's…