Don't have the *arr stack setup myself, but as to managing a library of of releases with both English and French dubbed audio I've found that looking for releases with 'Multi' in their names to be a relatively effective solution, though in trying to find releases on a handful of public French trackers looking for releases with 'VFF' (didn't see standalone 'VFQ' releases, though some VFF releases have VFQ audio tracks included as well) worked in that case as well. This seems to only work for popular movies, however, with TV shows and less popular movies, while sometimes being dubbed into French, seemingly not having those audio tracks anywhere I've looked (suggestions for good French torrent trackers would be welcome!), with the likelihood of finding English dubbed audio for releases originally in French appearing to be even more remote.

If you find a release with both audio tracks but want to use them with the video track of a better optimized monolingual release of the same movie, if the video tracks of two releases are the same length, or you can determine the exact offset between them, you can use MKVToolNix GUI to re-encode your preferred combination of video, audio, and subtitle tracks. A bit tedious compared to the automation of the *arr stack or simply keeping the default multilingual release of a movie, but at least it allows for fine-tuning individual releases on an as needed basis.

If you decide to make use of usenet at some point, I've found that some usenet indexers, such as NZBGeek, show in their search results the languages of additional audio tracks included in multilingual releases.