Dear Viking,
As you know, St Vladimir of Kyiv was of Viking stock as were the rulers of northern Rus' - we need more of the Viking worldview and less of the romanticized one that tends to dominate the Ukrainian character!
The tensions there between RC's and GC's are about the national tensions over the last several hundred years.
Poland dominated western Ukraine and attempted to assimilate the Ukies to become Polacks. The Union of Brest was most definitely seen by many Polish circles to be an instrument of a more general Polonization effort - and this proved quite true with the onset of Latinization later on.
Polish nobility entered the Basilian Order en masse and the Jesuits reformed it to the point where it barely resembles the ideal of the rules of St Basil the Great today (they are in fact Canons Regular).
But the Greek-Catholics held on and with Metropolitan Andrew Sheptytsky at the helm of their Church, the Greek-Catholics led the way to a renaissance of Ruthenian identity that later became focused on a staunchly nationalistic movement.
Russophilism also became dominant in the UGCC at the turn of the 20th century and to this day the liturgical publications by the UGCC at Rome are characterized by a heavily Russified language (according to Met. Ilarion Ohienko of the UOCC - something he pointed out to criticize the prevailing view that the UGCC was "superior" to the Orthodox on this score).
In 1648, when the Kozak Hetman Bohdan Khmelnitsky began his campaign to liberate the Ruthenian/Ukrainian lands from Polish domination, the Poles arrested Athanasius Filipovich the Ihumen of Brest and tortured him for several days to make him become Catholic. He refused and was then shot and buried alive after digging his own grave.
It is telling of the situation that St Athanasius, an Orthodox Venerable Martyr, became a hero venerated by both EC's and Orthodox. It is also telling that St Josaphat's early cult was heavily promoted by the Polish King and everyone in Polish society down (as is also unwittingly depicted in the quotes in support of his canonization that the Basilian biography of him lists).
Just as Ukrainians in Eastern Ukraine were called "Little Russians" by the Muscovite Great Russians, so too were the Ruthenians/Ukrainians of western Ukraine called "Little Poles." The old calendar, the three-bar Cross and other such symbols took on a symbolic, cultural character that identified the Ruthenians/Ukrainians and set them apart from their RC masters (the three-bar Cross was in even wider use in the Carpathians and anywhere where the foreign RC's attempted to culturally assimilate the people than anywhere in the eastern regions).
To this day among many Ukrainians and others, the new calendar is called the "Polish calendar" etc. At the time of Met. Andrew Sheptytsky, it was a common practice for the local Polish authorities to cancel insurance policies for Orthodox churches in Volyn, near Poland, and this was done so hooligans could burn the wooden churches and the people would not be able to rebuild them. Sheptytsky twice went public in protest against this treatment of the Orthodox (and he refused to continue the shameful legal process over who owns the Pochaiv Lavra that went on for years before he became the Metropolitan).
Although the two RC and GC hierarchies are at peace in E. Europe, the tensions at the parish level continue.
My mother was brought up a Roman Catholic and when she taught my brother and me to make the Sign of the Cross, she taught us in the Latin way.
The very next day when my father saw us "waving Latin flies away with the whole hand" (

) he was visibly shaken and afterwards worried about the impact that that early Latin experience would have on his two sons . . .

Alex