Curly's right you need to check the waiting period, but also check whtehr it will fall under general dental or major dental.
I think this depends on whether its a normal dentist or an endodontist who does the RC

Also depending on the level of cover you have, your insurance may not cover as much as you imagine.

We had the second top extras coverage (with Australian Unity) and DHs molar root canal still cost over $600 (with a general dentist)- then they said they couldnt save it and extracted it anyway!!

The out of pocket costs I was quoted for an endodontist, albeit an extrememly good one, was about $1500 + a crown which is about another $1000

ETA: Ive just realised that probably doesnt help you a lot.
The % of the total cost that we got back was less than 20%