Good to hear. Did you have to call the MP's office / congratulatory letter arrived without you asking for it?About a week after I got my citizenship, I moved to a different riding, and my new MP sent me the certificate and the congratulatory letter about 3-4 months after I moved to the new place. It's a nice thing to have, but I doubt it has any legal significance (though I wonder how much more of a hard time I would be given at the border if I present this certificate instead of a passport or the actual citizenship certificate).
As for entering Canada, I think this letter won't suffice for an immediate admission. You may be taken to secondary for identity verification. Moreover, airlines won't allow you to board the plane without a passport / other travel document.