Rome city officials expect up to five million people to attend the mass that will turn John Paul II, who led the Catholic Church from 1978-2005, and John XXIII (1958-1963), into saints.
Besides the www.2papisanti.org official website, the Vatican has set up several Facebook pages using the 2popesaints theme, as well as accounts on Twitter (@2popesaints), Youtube (2popesaints) and Instagram (#2popesaints).
Spokesman of the Holy See, Father Federico Lombardi, did not rule out that Pope Emeritus Benedict XVI would attend the ceremony on April 27 in St Peter's Square.
And while he gave no definite forecast for the number of attendees - pegged as high as seven million by some Italian media - he said that all pilgrims would be welcome.
"No tickets will be sold. Don't ask the prefecture as there will be none," he joked.
The twin papal canonisation will be the first in the Vatican's history and is expected to appeal to both wings of the Church.
John Paul II, the first non-Italian pope for more than 400 years, was a favourite of conservative Catholics and his canonisation will be one of the fastest in recent history.
Pilgrims are expected especially from his native Poland, and many hotels in Rome are already booked out.
John XXIII is also widely admired by the Church's progressive wing for calling the Second Vatican Council that transformed the Church.
An all-night prayer vigil will be held in seven languages in 11 churches the night before the ceremony.
"A common thread connects the two popes, their faith," noted Cardinal Vicar of Rome, Agostino Vallini.
-AFP, Vatican City