C# :: How To Use Confirmation Dialog When Reading Strings

Here's what I want to do:

So, basically the user imports a list of strings from a CSV file and the lines get read line by line and sorted in a listbox. If the user uploads the same file again that contains the same list of strings, a confirmation box with the following is supposed to be displayed:

"The list is the same. Are you sure you want to import this list of strings?" The options are yes, no, maybe.

If the user clicks on yes, all the strings get saved/put into the listbox regardless of whether or not they are repeated. No allows the user to to cancel the whole operation and return back to the screen for all samples. Maybe allows the user to individually pick which one they want saved or not. Maybe takes the user to a yes or no confirmation dialog box and it loops through all the strings in the csv file until the user has picked yes (accept) or no (deny). Only the confirmation box with yes and no should be looping.

What I have so far:

-Two confirmation boxes (I decided it would be easier for me to create two views and two viewmodels just for confirmation box setup - one with confirmation box of yes/no/maybe and one with confirmation box of yes/no).
-All the event handling is set and done.
-Reading the CSV file and checking for duplicates.
What I have problems with:
-When the call the confirmation dialogs...

Here's a snippet of what I have:

public void ReadImportedSamples(string filePath)
{
string line;
try
{
using (DDataContext context = new DDataContext())
{
using (StreamReader sr = new StreamReader(filePath))
{

[Code]...

So, I have two confirmation boxes, confirmationWindowSamplesListYN (only yes and no) and confirmWindowForSamplesList (with maybe).

Everything is set up fine. I am just wondering when the call the proper confirmation dialogs so that I can get the behavior above?