Would an inlay be an appropriate choice for a tooth with a root canal? And what material would be best for a back molar?

Hi:
The best restoration to protect the tooth after a root canal is a crown or onlay not an inlay.  The cusps have to be protected against any fracture due to brittleness of the tooth after root canal.
Best,
Dr. Maddahi

Hi there,
An inlay is not a good choice as it does not support the cusps of a more brittle root canal treated tooth and there is a greater risk of fracture. A vertical fracture of a tooth can render it non restorable and may require extraction. 
An onlay covers and protects the tooth and lowers the risk of fracture while retaining a good portion of your natural tooth so is more conservative. The more aggressively prepared crown also does this and would be a good idea when there is limited tooth structure left and the protection from tooth fracture is the highest priority.
Hope this helps!
Best regards,
Dr. Ed Lowe

With a root canaled tooth, you want something to cover the chewing surface of the tooth. An onlay would work, but an inlay would only make the tooth split in half and need an extraction. An onlay is a much more conservative option than a crown.