If my opponent cancels Meera Reed (usually with Seasick), does she remain in shadows or remain in play? I assume that 1 gold is paid and nothing is blanked either way.

You pay the gold TO bring her out of Shadows, then blank stuff. So coming out of Shadows and into play is an effect, not a "cost" of then blanking effect. If you cancel, ALL effects are canceled, so Meera would not come out of Shadows.

Can be meera cancel for vyman or throne lannister? i read time ago that meera cannot be cancel for card that cancel habilitys of characters, its true? the gold back if its cancel?

The part of Meera's effect that is a character ability is after the word "then". That means it's not possible to cancel this part alone. You need to cancel the first part, which has no target and is not a character ability, so neither Maester Vyman nor The Iron Throne are valid cancel responses. What you need to cancel Meera's coming out is a generic triggered effect cancel like To Be a Kraken.

And no, you don't get the gold back if Meera is canceled. Just like you don't get to put an event card back in your hand if it is canceled. When an effect is canceled, the costs stay paid.

Khudzlin said:

But vyman cancel triguered in stark characters, if mera choose a stark character to blank i believe he can.

orion_kurnous said:

You cannot cancel an effect based on the chosen targets from the "then" effect.

The targets that are chosen using a "then" effect happen after the "save/cancel" opportunity.

Specifically, before Meera is allowed to choose a target character to blank, she must have come fully into play. We know this because her text says " Then choose…," and before anything after the word "then" can happen, the part before the word "then" must be complete and successful.

And, as the FAQ states, there is no opportunity to cancel the stuff after the "then" (although special permission is given to save things from stuff after the "then"). So Vyman will never be able to cancel Meera because the target that needs to be chosen to satisfy his play restrictions will never be chosen until after the opportunity to cancel the effect has passed.