I can't speak to Finland and Sweden, but in Ireland, English was pretty heavily enforced as a language by the British colonists. Irish was prohibited in British National Schools, and the famines hit the rural areas, where Irish was a majority language, much harder than urban areas where English was more popular. There's also the fact that English naturally presented more opportunities as a high-esteem language.

Religion pretty much was adopted from Britain in Ireland. Roman Catholics brought it over in the 5th century. The English reformation was just much harder to enforce later on, as Catholicism had become a large part of the Irish identity. It's much harder to convert people when they don't speak your language, and while many English speakers in Dublin (and obviously Ulster) were Protestants, Irish speakers remained Catholic.

Daniel O'Connell is a pretty famous Irish historical figure who championed Catholic Emancipation during the 19th century. He founded the Catholic Association which campaigned for and succeeded in getting the Catholic Relief Act passed in 1829. The act allowed Roman Catholics to sit in Westminster and generally signalled the turn of public opinion against the persecution of Catholics in previous centuries.

As a Finn, I am going to have to point out that we did in fact adopt the swedish language. Of course, the common peasant would still speak finnish, but the language used in government, legislation and such was exclusively swedish for several hundred years. To this day it remains by law our second domestic language, which means every child has to learn it in school and all government services have to also be available in swedish. Even today over 5% of the population of Finland (mostly on the southwest coast) speak swedish as their primary language.

Also, any attempts from Sweden to further solidify their language's position in Finland were thwarted in 1809 when what is today Finland was taken over by the Russian Empire. They in turn later attempted to assimilate Finland and force Finland to adopt their language and religion, but these attempts weren't very effective, in no small part because at that time Russia was already heading into the October revolution.

Michael C. Coleman examines this very question in an article titled "‘You Might All Be Speaking Swedish Today’: language change in 19th century Finland and Ireland" in the Scandinavian Journal of History.

In it, he makes the case that these two factors are indeed linked. A central idea in Lutheranism is that everyone should be able to read the Bible, and in the Swedish Realm, the clergy would routinely inspect that their parishioners were able to read the Bible. He notes that thanks to the religious literature widely available in Finnish, even ordinary peasants were able to read in Finnish by the 18th century, although Swedish had the status of the language of the elite, of the bureaucracy, and of higher education.

He contrasts this situation to Ireland where the language used for Catholic liturgy was Latin. Although half of the island's population spoke Irish by the beginning of the 19th century, only a very small percentage of the speakers were literate in it. The national schools that were established in Ireland to teach the peasants only taught in English, which was also crucial for literature in Irish never becoming widespread. When Irish nationalist movements arose, even they would use English to publish their views.

Finnish-language literature and newspapers on the other hand played important roles in spreading the ideas of the Fennoman movement that tried to elevate the position of Finnish from a "language of the peasants" to a language of higher learning. The 1835 publication of "Kalevala" in Finnish is regarded as an important milestone in firmly establishing Finnish as part of the Finnish cultural identity. The movement was successful, and by the time of Finland's independence, Finnish had supplanted Swedish as the dominant language in higher learning.

The relationship between Sweden and Finland has its roots in the Christianization of Northern Europe during the 12th century. As the Kingdom of Sweden began to form a distinct common cultural identity, the early Swedish kings embarked on a number of regional conquests ostensibly in the name of a crusade. By the late 14th century, Finland had become entrenched in the Swedish Realm with its own nobility, representation and government. After the fall of the Kalmar Union under Gustav Vasa, Finland began to drift closer to Sweden by mirroring its cultural and religious practices.

The real change in culture came during the Finnish War of 1809 when Gustav IV was forced to cede Finland to Alexander I of Russia. Alexander I used Finland as a testing ground of sorts and called the Diet of Porvoo in order to summon the Finns to pledge their allegiance. At Porvoo, Alexander I promised to allow the Finns the right to worship freely thereby resulting in a Lutheran Finland.

After the annexation of Finland into Russia, the language of administration became German in an attempt to culturally shift Finland away from Sweden and to avoid using the language of their enemy. Translators were soon employed and the number of Russian civil servants grew as St. Petersburg tried to consolidate its conquest. Since German wasn't the local tongue and Russian too hard to teach in such a short time, the administration eventually decided to encourage the use of Finnish -- then a peasant language -- throughout the country. Finnish was therefore arguably revived and standardized in Finland while the religion of the people remained the same.

Edit: For a source, please see this post here.

One major difference that shouldn't be overlooked is that Christianity was introduced to Ireland already in the 5th century, whereas in Finland the earliest Christian items can be placed to the 9th century from grave sites at that time and on historical records it can be said to have been introduced earliest at the 11th century.

From this it could be said that Ireland didn't adopt Anglican Protestantism because Catholicism already had strong roots, whereas the time period of Catholicism being the major religion in the whole of Finland was relatively short as Kingdom of Sweden ruled only the Southern parts of Finland. Most of the Northern Finland wasn't part of the Swedish rule, for instance Northern Karelia started to have significant habitation only in the 16th century and by that time Sweden also became Lutheran.

Being the one of the last countries Continental Europe to be converted into Christianity old pre-Christian religious habits in Finland were difficult to get rid of completely. Pagan beliefs and rites in one form or another remained relatively strong in one form or another still in the 16th century during and after Lutheran reform, Mikael Agricola the Bishop of Turku publishing a list of pagan deities the people in Häme and Karelia still worshiped at that time.

So in one way, Finland didn't exactly adopt the religion of Sweden or the language, both were practiced more by the Swedish people who had settled into Southern Finland, but as both belonged to the customs of the ruling class, they were learned to a degree. Even still, religious practices were partially only paid lip-service, and the majority of the common people never adopted the language enough to forget Finnish.

England too was Catholic when it took over Ireland. Irish missionaries had even been engaged in restoring Christianity in Anglo-Saxon England centuries before. So some northern parts of England adopted the religion of Ireland while the south took its lead directly from Rome.

Not sure if anyone has noted this or not but the English outlawed the Irish language which certainly didn't help the native tongue. In the Western parts of Ireland one can find areas where it is used almost exclusively.

Sorry if I'm late to the party.