That Canada has a high rate of MS is consistent. The further north or south you are the higher this risk. In a country with a high rate you should not be surprised by some clusters just by chance. That does not mean it should not be investigated.
I am rereading Osler's Web. One of the first stories is about an MS cluster outbreak of MS in Miama, which is a warm sunny clime. This was regarded by many as simply wrong, as the doctrine is that MS does not cluster, even though people went to Miama from all over just for the climate. I think the upshot of this is that they mostly had ME, not MS, but I forget the details as I read OW a very long time ago now.
One study I read of a while back, however, went looking for causes of childhood developmental problems in Mexico. I forget the details now, its been years. They found no match with any chemicals etc. However they looked at chemical usage, I think it was pesticides, and found that the areas that used a particular combination, two pesticides I think, matched the locations of these childhood developmental clusters. One of the things that investigators can get wrong is they do not look at how chemicals and other factors combine. Its a combinatorial problem. We just don't have good enough technology and science to do this reliably yet.
We know there are different types of MS. The first thing I would want to know, if I saw an apparent cluster outbreak, is were they mostly the same type?