Follow-up. I made some preliminary measurements using my 11iSis and a 700 (100 x 7) patch grayscale target for all three Canson Somerset Papers. The results are as follows:
Canson Somerset Enhanced Satin: Dmax = 1.82, Lmin = 12.730, Lmax = 98.107
Canson Somerset Enhanced Velvet: Dmax = 1.82, Lmin = 12.629, Lmax = 97.679
Canson Somerset Enhanced Watercolour: Dmax =1.82, Lmin =12.754, Lmax = 97.681
As you can see, the three papers have very similar performance. This would seem to indicate that all three papers are likely using the same coating. Also it should be noted that my measurements correlate very well with the Epson P900 profiles supplied by Canson with respect to Dmax. It is possible that with additional linearization and optimization you could expect an even slightly higher Dmax and a slightly lower Lmin than what is shown here. In summary, I believe all three papers should be consider when printing fine art B&W prints.

They perform very similarly to Canson Arches Aquarelle, BFK Rives and Arches 88. As a point of reference, my fully linearized and optimized measurements for the older Canson papers are as follows:
Arches Aquarelle Rag: Dmax = 1.84, Lmin = 12.271, Lmax = 96.657
Arches BFK Rives Pure White: Dmax = 1.83, Lmin = 12.434, Lmax = 96.3
Arches 88: Dmax = 1.83, Lmin = 12.433, Lmax = 96.568