Based on what I have been told, various big European retailers are expecting first EOS 5DS and EOS 5DS R batches more or less by the end of next week/beginning of the week after. Guess this is valid also for other retailers around the globe, especially in the USA.
Keep in mind that shipping dates may also be delayed because of unexpected issues. However, I am pretty confident both the EOS 5DS and EOS 5DS R will start shipping all over the globe from mid June, with some delays to the last June week for smaller countries or markets Canon considers not a priority.
Canon EOS 5DS: Amazon USA, Amazon CA, B&H Photo, Digitalrev, eBay US, Adorama, KEH Camera, Canon USA, Canon CA, BestBuy | Canon EOS 5DS R: Amazon USA, Amazon CA, B&H Photo, Digitalrev, eBay US, Adorama, KEH Camera, Canon USA, Canon CA, BestBuy