Also just found this from the Ontario Highway Traffic Act:
Noise, smoke, bells and horns
75. (1) Every motor vehicle or motor assisted bicycle shall be equipped with a muffler in good working order and in constant operation to prevent excessive or unusual noise and excessive smoke, and no person shall use a muffler cut-out, straight exhaust, gutted muffler, hollywood muffler, by-pass or similar device upon a motor vehicle or motor assisted bicycle. R.S.O. 1990, c. H.8, s. 75 (1).
Unfortunately, the "straight-through" design of the Roush mufflers could be interpreted as "straight exhaust". You might have a tough fight ahead of you.
If the ticket was for noise, then you most likely violated a local bylaw, not the HTA.