LensRentals did a resolution test of Sony FE 90 mm F2.8 Macro G OSS using their Imatest lab, comparing it with Canon 100mm f/2.8 IS L.
Their conclusion is that the new Sony 90mm f/2.8 G OSS Macro seems to be a superb addition to the E mount lineup, and the lens on an A7r should provide superb resolution.
According to them it seems that Sony lens performs at least as well as the Canon 100mm f/2.8 IS L, from a resolution standpoint.
Read the full article at LensRentals.