Best of Luck fighting City Hall.
My first recommendation is know specifically what the law says and in whose jurisdiction is it. You said its a "local bylaw". Does that mean that the Ontario city council would have the power to change it? Be sure to know precisely which governing body can change the law. You can probably find all your local law and regulations at the library or possibly online. know the exact text of the law. You need to go the government with exactly what you want changed. is the law too generic and overarching? Does it ban all boas and pythons, including something like a ball python when they really intend something more like a green anaconda? Perhaps the law should be amended to only specify a few species rather than an entire category. What was the concern in making the law in the first place?
Do your research and be prepared to address opposing concerns. Be knowledgeable on the subject. Perhaps the law is completely unnecessary. Be prepared to present evidence of your claims. Have hard facts at hand.
If you can attend city council meetings before hand, do so. Its helpful to know who you are dealing with and who you are pleading to.
The more support you can gather for your cause the better. How many herpers are in Ontario? Are there any clubs or organizations. How many people does this law effect? As far as I know, Ontario Canada isn't a small two horse town. You can probably get a lot of support to overturn this law. How does it affect local business? Are there any reptile expos in Ontario? Perhaps this law drives away business (taxes)? Are local petshops prohibited from selling an item that they should be able to sell. When you actually go to a meeting to propose your law change, bring as much support as you can. Have a peaceful show of support can influence their opinion, even if your support never speaks and only takes up space.