I reached out to Canson Infinity US. They stated they expect the ARCHES papers to arrive mid-June from France. I assume they then need to ship to their distributors, such as B&H. So my guess is 4-6 weeks for the US.
Since the papers are manufactured in France, it would seem Europe might get the ARCHES papers a few weeks earlier.
I did not ask about the matt baryta.
-Tim