Antique has the "que" in it which is a Spanish root.
Canoe has the root "oe" in it.
And Coyote has the Spanish root "ote" in it.
Therefore, POTATO, does not have a Spanish root.
Think of how it is said...we don't say Coy-Oat, we say Cai-Oh-Tee, so the spelling is very different to the spoken word.
(hope that helps a little)