Lemon, on Markham Main St, is pretty good - http://www.lemonbistro.com/lemonbistro/wikiData/lemon/Home.jsp - although I don't know if they are open for lunch.
And it's nothing spectacular but I have always enjoyed every meal I have had at the Blacksmith's Bistro on Unionville Main St http://www.blacksmithsbistro.com/
166 Main St, Markham, ON L3R, CA
Main St Cafe
13 555 Simcoe S, Oshawa, ON L1H8K8, CA