Yup - I was thinking Fahrenheit. Twenty lashes for me on not picking up on the "tinned" reference - especially since I have a friend who lives in England - lol!!
That said, your idea of adding beans to this casserole is absolutely PERFECT!! However, I'd gently fold in the drained beans during the last 1/2 hour of cooking. That's all the "cooking" they'll need & will give them more than enough time to absorb the other flavors. Cannellini beans in particular have a very thin skin.
Do come back & let us know how it turned out. Sounds delicious.