'Migrant' indicates movement but not direction. Migrants move but we don't focus on where to or where from. 'Immigrant' indicates movement and direction. An immigrant moves INTO a place. Immigrants in Canada have all moved into Canada. An emigrant is someone who moves out of a place. The UK has quite a lot of emigrants. This means that many British people move out of the UK to live in other countries.

With the word ‘migrant’ there is a sense of people moving from place to place, not staying long in each one. It’s often associated with seeking employment that is seasonal, e.g. migrant farm workers.