While it's likely the one wearing Kouya will be the muscle of the team, I feel like this character could be the unexpected tanky and heavy defense type looking at what I assume is a shield on the back of the armor.
As for voices, a comment on Reddit suggests that Ayumu Murase may voice the Suiren wearer and Junya Enoki may voice the Soukyuu wearer, which, judging by the initials that were revealed and tone of the voices, seem very likely. My guess for Kouya and Senkou at the moment are, respectively, Shunsuke Takeuchi and Kentaro Kumagai.

Suiren's definitely keeping his predecessor's versatility - hopefully he'll use it more too. The shield is an interesting touch, I hope it's not another case of the water character being relegated to a defensive/support role, and it's definitely something different. Not really a fan of him using a short sword instead of a spear but then my bias is legendary. What really catches my eye is that the claw on Suiko's right arm seems to have been replaced by what looks like a hook.

https://i.postimg.cc/GpPGJN86/CDK-rajura-web1.jpg
https://i.postimg.cc/FRDSwLxZ/CDK-rajura-web4.jpg
https://i.postimg.cc/j22fTSgr/CDK-rajura-web7.jpg

Oh that's the stuff right there.