[wparsons]

There's no regular emissions tests in Ontario any more, but if you're stopped by the MTO (or a cop that calls in the MTO) they can do a roadside sniffer test in addition to a visual inspection and fine you for removing emissions equipment. If you keep a cat in the front pipe you're less likely to be noticed because it'll keep it from smelling like you're catless, but if they look at the header and notice there's no cat there you can still be fined. Technically you can even be fined for replacing a stock cat with a high flow one, but if there's a cat where there's supposed to be I doubt any officers would notice if it's stock vs aftermarket.