I thought the Kanon dub was pretty good. Especially Ayu and Yuichi’s VA’s. Actually, to be completely honest, the "Key"o-Ani Trinity has the better dub’s compared to the later Key dub’s.
As far as I know, there has been very-little dub’s where they dub the music. It’s not really worth dubbing the music anyways, since dub’s usually won’t ever release the actual English-version of the song, so it’s pretty much useless to dub the songs when they’re better off without dub, and with the very fact that they won’t be selling it.
Even if there’s a chance they do dub the music, they would only dub 3 tracks, and those would be from How-Low-Hello, which played in the anime. The rest are ZHIEND songs and they already have English vocal versions.
There’s also the OP/ED which won’t be dubbed no matter what, and Kimi No Moji, which wouldn’t be dubbed anyways, cause no English singer could convey the feelings that Anri Kumaki put into that song, having a soft-tone, beautiful voice, calming-nature, and very-fitting voice.