If you want a really flat 600K Randonneurs Ontario is having one out of Windsor, Ontario which is a super-flat area... the
windsor 400k only has 541m of climbing and there's not really a lot of hills in the next 100km in any direction. Our schedule isn't posted so I don't know when it is happening but I'd guess June. Probably a bit too much a drive from PA though. Other ontario 600s start in Toronto and aren't as flat but also probably not as hilly as PA is. There's a devil's week happening out of Toronto next year too... end of May I think.