On Remembrance Day, I would have absolutely no objection to “I Vow to Thee My Country” as a recessional.As a Canadian, I would personally be fine with both O Canada and God Save the Queen *after * holy mass on special occasions - say on or near Remembrance Day, Victoria Day, or Canada Day. Both the national anthem (O Canada) and the royal anthem (God Save the Queen) include implied prayers to the Christian God, so not completely inappropriate.