We rode a total of three times and TYPICALLY, the cards were handed out in the order people were standing in, starting on your right, Pilot, Pilot, Gunner, Gunner, Engineer, Engineer. If you are thinking "hey does this mean single riders will almost always get Engineer?" yes, yes it does. On our first ride, a CM called down the line for a party of two, which I have a near Pavlovian response to, so we went forward and got (surprise!) the two engineer cards. My BF, who does terrible on motion sim rides like Star Tours actually really liked being engineer. To quote him "spent so much time pushing buttons I didn't notice to get sick!" I found engineer to be entertaining, something was typically breaking down during that ride as our pilots had a habit of missing button pushes, whoops!
On our second go we were the front pair, but I realized we had some antsy people so as soon as the CM started the "Hondo is looking for some pilots, gunners, and-" spiel, me and TWO other people (we were three sets of two) piped up wanting to be pilot. This was during one of the wait time walk on moments, so the CM asked the last pair to wait for the next mission, and myself and one young lady from the other group were the pilots (I was on the left, in fact I never got to sit on the right for any of my rides!) BF took gunner, which he didn't like as much as engineer and he found aiming to be a pain and advised me to pick auto aim if I was ever a gunner. We didn't do TOO badly that time (I hit the buttons!) Oh! We also had auto-engineers engaged, though I think the gunners now had harpoon control? Not sure, I was busy dodging left and right
Since we ended up being locked out of the cantina (whoops again), we went for one more ride, with me hoping to get gunner. They called for a party of two, but I didn't volunteer this time (cause see above, engineer) and we were in fact in front of a family of four, so we SHOULD have gotten the pilot cards and been able to trade. ALAS, the kids were either wise to this, or just couldn't stand still, because they snaked around us quickly, and the parents followed them and suddenly we were engineers again. Lucky for me, the mom of the group was will to trade with me. (When I first asked to trade with one gunner, one of the boys started yelling that he wasn't giving up his card... Like umm, plz chill? Same child also shoved me to the left side of the Falcon because he suddenly decided he wanted to sit behind Dad and not his brother, which you'd think would hurt being able to see, but the mind of a child...)
Regardless, I found engineer more fun than gunner (though I did auto aim). And yes you can just hold down the button, but your final payout will be docked for wasting ammo! Hope this helps!