"La junta para discutir los nuevos carriles bici fue cancelada." To simplify the above sentence, one may imagine to drop out the infinitive clause, and the sentence becomes, "La junta fue cancelada." Now one can easily see why it should be written as "cancelada" but not "cancelado". In terms of the passive voice, it is always expressed with "ser" and not "estar". Thus, here comes with the above sentence. === Deseo que tengas un buen día.／I wish you a good day.

Hello, Martyn. The above answer is correct, so I will just provide a few more examples. The noun of the adjective "cancelada" is "junta", as explained before. That is why the adjective has to be in feminine. Most Indo-European languages use the past participle as an adjective derived from a verb. Yo vendo la ventana. (I sell the window). Yo vendí la ventana. (I sold the window). Yo he vendido la ventana. (I have sold the windows). La ventana es vendida en diferentes tiendas (the window is sold in different stores). Now, you can use the verb "estar", but that would imply that it is not a passive voice anymore, you would be describing a state (which the verb "estar" is used for). La ventana ya está vendida (the window is already sold). I hope this is of help.

Hola Martyn; como ya han dicho mis compañeros el adjetivo "cancelada" se refiere a "junta", no a carriles bici. Por otra parte "cancelada" es un verbo para designar un paso definitivo, no susceptible de evolución posterior, lo que hace que convenga el verbo SER, mientras el verbo ESTAR se aplica a cosas cuyo estado si puede cambiar todavía.