Can they? Sure. Christians can, as all humans, oppose or support migration however they choose. "Should they?" Is a more difficult question. Christians, by definition, are followers of Christ-based religions. Most Christ-based religions have several factors in common. Some of these factors include loving others, helping those in need, feeding the hungry, clothing the poor, loving thy neighbor, remaining unjudgemental, and extending assistance to those who need it, even those who you may not agree with or understand. By those tenants, Christians should support and assist migrants. However, in practice, it is not so cut-and-dry. Many Christians (though, certainly not all), are politically conservative, and many conservatives (though, again, certainly not all), oppose immigration and migration.

It's not in the spirit of Christianity to oppose migration. However the number of practicing or as the Americans might say card carrying Christians mabe a lot fewer than those brought up or educated in the Catholic faith. Number have been dwindling in Catholic churches for quite some time and many wonder how another generation will practice catholism publically if at all.

These softer forms of religious connectivity does leave a gap open for those to pick and mix which parts of their religion they enjoy....Christmas celebrations etc and igore Christian values such as tolerance.

Therefore it's very unlikely for priests of active Christians to oppose migration but they are most likely very much in the minority of those that might classify themeselves as Catholic or Christian on lets say a census or a Government form