When I intend to marry, must I travel to Turkey for my praying maternal uncle to be my guardian, or is it better to nominate one of the imams of the mosques or Islamic centers in Finland to be a guardian?

For a marriage to be valid, the presence of a wali (guardian) is a condition. A disbeliever has no guardianship over a Muslim woman. Guardianship belongs to the paternal agnates. The maternal uncle (khal) is not a wali, unless he is appointed as an agent by the wali, or if the marriage contract was concluded and documented in a country that permits this. If there is no wali, a Muslim judge marries her. If no judge is available, then in Western countries, the head of the Islamic center, or the Imam of the mosque, or a scholar, or a just man from among the Muslims marries her.