I associate the name Dundas with the street in Toronto (and Ontario) which itself has important historical and cultural importance to me as a Torontonian and Ontarian.
I don't know who Lord Dundas is and I couldn't care if the street that I grew up associating downtown Toronto with was initially named after him.
Renaming the street today however, feels like a removal of Toronto history given how important the street has been to our understanding of Toronto's physical, social, and cultural development.
If this is such a pressing issue to resolve however, my compromise suggestion would be to rededicate the street to another person named Dundas with a more palatable set of political beliefs. I am sure someone could be found, one likely doesn't even need to look far given that Lord Dundas was a title not a person.