plans to marry at 2009
plans to marry on 2009
肯定错
plans to marry in 2009
plan to marry in 2009
就要看你的主语了
he plans to marry in 2009
they plan to marry in 2009
但,就地道的说法是
they are planning to get married in 2009
plan/plans to get married ..+ 时间
plans to marry sb
这种说法,就正确