I'll second the idea of Niagara-on-the-Lake. Very quaint town and worth a visit.

Although it's extremely touristy, a ride on the Maid of the Mist is a must while in Niagara Falls. www.maidofthemist.com/en/

It's always fairly busy in Niagara Falls, but October shouldn't be too crowded since the kids are back in school. Canadian Thanksgiving is Mon, Oct 11th, so perhaps that holiday weekend might be a bit busier.