Rome police expect up to five million people at the mass officially making saints of John Paul II, who was pope from 1978-2005, as well as John XXIII (1958-63) in the first double papal sainting ceremony in the church's history.
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).
Vatican spokesman Father Federico Lombardi did not rule out that Pope Emeritus Benedict XVI who was a close confidante of John Paul II would attend the ceremony on April 27 in St Peter's Square.
While he gave no definite forecast for the number of attendees pegged as high as 7 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.
John Paul II of Poland, 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.
At his funeral in 2005, hordes of pilgrims chanted "Santo Subito!", which loosely translates as "Sainthood Now!"
Many Rome hotels are already booked out for the canonisation mass, and an all-night prayer vigil will be held in seven languages in 11 churches the night before.
John XXIII is also widely admired by the Church's progressive wing for calling the Second Vatican Council, or Vatican II, which introduced key reforms.
"A common thread connects the two popes: their faith," noted Cardinal Vicar of Rome, Agostino Vallini.
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