It looks like MTF will be the first company to bring a full series of Canon RF mount adapters to market.
All of the adapters from MTF are made from HE30 aluminium with a stainless steel seating face. All adapters come pre-shimmed for accuracy and will include spare shims just in case you need them.
MTF R Mount Adapters:
PL to R Mount
Panavision to R Mount
ARRI Bayonet to R Mount
Canon FD to R Mount
Nikon G to R Mount
B4 to R Mount (providing S35 mode on the camera)
Pricing and availability have not yet been announced.