Canon’s older 5D series of mirror slapping cameras is known to take abuse pretty well. Shooting an R5 over a marsh in the rain this morning showed that at least one of the new mirrorless version of the 5 series, the R5, appears to perform similarly.
Weather sealing isn’t really a yes or no feature. It is something that happens by degrees, and camera manufacturers are careful to be cagey about it, lest they inherit specific liability for cameras that suffer any leaks.
The original EOS R was billed by a few Canon USA executives as a 5-series equivalent after it inherited the sensor from the 5D Mark IV (albeit 4 years after that sensor was introduced), but users of both cameras quickly came to understand the R had more limitations. In the weather sealing area, an obvious one was the fact that the grip was only partially sealed. Oddly, the R’s BG-E22 grip was sealed around the data port between grip and camera, but not sealed at all where the insert fed into the battery cavity. One would have thought they’d seal either both or neither. The R5’s grip (tested the WFT R10A version) is sealed in both places.