There is an ongoing debate, and a great deal of interests in regionalizing immigration. Most immigrants are concentrated in urban centres and they are being encouraged to move out into the regions. This has been going on now for 25 or 30 years. There have been successes, but there have also been failures. If you can understand why immigrants settle in large urban centres, then you will have gone a long way towards answering the question.
There are many factors to explain this phenomenon, and I will venture my own theory on the matter. A number of bilingual immigrants belong to what we can call our pool of francophone immigrants. These people are often surprised to see that almost everything is done in English. There are also a number of unilingual francophone immigrant who are encouraged to settle in communities but who realize that they can't function because they don't speak English. These are undoubtedly some of the factors that would cause unilingual francophone immigrants to chose homogeneous francophone areas to settle in.