Interesting that you did not get a reply either.
I have sent two letters by postal mail to Air Canada this year, in both cases to recognize excellent service that I have received, and have not received an acknowledgment for either one.
But, whenever I send an email to the Super Elite email address, I always get a response within 24 hours.
It is kind of frustrating to take the time to write a nice letter, to draw to the airline's attention someone who has really been "the best of the best", and not hear back. My only concern is that the employee was not given the commendation that they deserved.
I think that this is one area that Air Canada needs to look at.