It depends on how you want to qualify that. In the comic, Canada is said to be older. This is presumably because of a) below.
a) If you go by settlement, Canada, as it was a settlement before America - L'Anse Aux Meadows, etc.
b) However, if you look at independence dates, America would be older because Canada gained its independence on July 1, 1867, whereas America gained its independence on July 4, 1776.