I was writing an email to the principal of my former school, and I [came up with / had come across] a question: "Shall I write "Merry Christmas" or "Happy New Year" at the end of the letter?"
Which phrase should I use?
I was writing an email to the principal of my former school, and I [came up with / had come across] a question: "Shall I write "Merry Christmas" or "Happy New Year" at the end of the letter?"
Which phrase should I use?
To come up with something means to create it or originate it. If you made up the question, this is the correct choice.
To come across something means to find something which already exists. If you did not make up the question, but instead found it elsewhere, this is the correct choice.
Either way, don't use the pluperfect had come across, just came across.