Called to Arms - opponent discard 1,2 or 3 cards from top of the deck to give 1 of 3 effects to the GJ player.

If I have any number of Motley Crewmen can I force that same opponent to discard extra cards equal to my Crewmen?
If so does it mean that the opponent declares which numbered effect he's allowing the GJ player to have then discards additional cards or for example if there was 2 Crewmen in play could he discard 1 card followed by 2 more for my Crewmen and I still get the '3 card' effect.

My apologies if that's confusing.

Thanks in advance.

Pretty sure you still only get the 1 card effect. He maybe be discarding 3 cards, but he only chose to discard 1. Called to Arms doesn't care how many are discarded in the end, but how many the opponent chooses.

Correct. The opponent chooses how many cards to discard - which defines the effect from Called to Arms - and then discards one more for the Crewman's effect.

Look at it this way: if you have 3 Motley Crewmen out and your opponent chooses to discard 1 card, they do indeed wind up discarding 4 total cards. But what effect do you then get from Called to Arms? There is no "discard 4 cards" effect, right?