I thought the same thing after looking over my shots and seeing the resemblance between these two riders... but after PM'ing BURRUS a bit he seems to think they were just friends and not sisters. It looks like he was there at the end of the ride so may have had a better chance to chat with them a bit. But the similarity between the two is uncanny! Hopefully he'll post more of his shots at a later date!
Regardless, they're both extremely attractive and seemed to be enjoying the ride

It was a lot of fun from what I saw. All the men and women I talked to in front of Nathan Phillips Square (where they stopped for a rest and photos), were having a good time and all smiles when I asked how the ride was so far. They all had very positive things to say about it