The Grand Ayatullahs say:
It is okay for a Shia man to marry a Sunni woman, but if he fears to be misguided by her, it isn't permissible.
As for where to contract the marriage, it doesn’t make a difference, although some might do it in a holy place.
This is the response to these two questions from the offices of the Grand Ayatullahs:
1- If a Sunni woman is married to a Shia man, are the children considered Sunni or Shia?
2- If a Shia woman is married to a Sunni woman, are the children considered Sunni or Shia?
The office of the Grand Ayatullah Khamenei:
In both cases, the children are Muslim and when they come of age, they have to choose between the two.
The office of the Grand Ayatullah Sistani:
Before coming of age, the children are considered what the father is, and afterwards, they have to choose for themselves.
The office of the Grand Ayatullah Makarem Shirazi:
1- The children have to do research and follow the true path, which is the path of the Ahlul-Bayt.
2- Getting married to Sunni men isn't permissible for women, if they fear to be misguided by them, or if they fear that their children will be misguided in the future.
Similar Answer: Marriage of Sunni woman with Shia man, Question 3535 (website: ).
 Ayatullah Vahid, Minhajul-Salehin, vol.3, issue 1298; Ayatullah Tabrizi, Minhajul-Salehin, vol.2, issue 1298; Ayatulah Nouri, Istifta’at, vol.1, question 668; Ayatullah Safi, Hidayatul-Ibad, vol.2, Al-Qawl fil Kufr; Imam Khomeini, Tahrirul-Wasilah, vol.2, Al-Qawl fil Kufr, Ayatullah Khamenei (istifta’), question 16 and 143; Ayatullah Makarem, Istifta’at, vol.1, question 708; Ayatullah Sistani, Minhajul-Salehin, vol.2, issue 215; The office of Ayatullah Fazel and Ayatullah Bahjat (narrated by Porseman).