The leaked spec sheet mentions aluminum alloy, but it's not clear whether it refers to the chassis or body. The 80D is polycarbonate shell with aluminum and glass fiber chassis. The 90D may or may not be the same.Minor concern over Magnesium alloy body (7DmII) v Aluminum alloy (90D) and the extent of the weather sealing on the 90D.
I wouldn't worry too much about the weather sealing. Even the 80D has, according to Canon, a level of sealing equivalent to the original 7D. The 90D sealing may well be similar to that of the 7D2.