Oh you can't avoid Buffalo if you're wanting to make it through the Niagara Falls border. What I meant was during the aftermath of the blizzard with I-190 near the actual city of Buffalo being closed, we had to drive through rural Erie and surrounding counties local routes on the trip down. But since the weather isn't an issue right now you'll likely take I-380, 86, 390, and 190.

If you really are keen on avoiding it for whatever reason then you'd have to enter the border through Kingston, ON which is a 3 hour drive from Toronto instead of the usual hour and 20 from Niagara Falls as well as having to trek up the northern portion of upstate NY