From what I have seen (last time 3 weeks ago), the nicest lounge at FRA is the Delta Crown Room next to gate D8, about 15 mins from where AC flights board (B). It is open from 7 am to 2 pm. Ask for Riccardo (Rick) who is very helpful.

In Halifax, there is only one AC lounge, very easy to find and fairly close to all gates. The lounge itself is quite large and nic.